Tag Archives: Vitamin D

 I'm starting to see studies questioning whether some of the beneficial health effects that many attribute to vitamin D may actually be due to sunlight. In the first study, researchers said that sunlight also has low levels of "blue light" which energizes T cells. T cells are a type of white blood cell, are part of the immune system, and help protect the body from infection and cellular abnormalities (cancer). So the blue light in sunlight had a positive effect on the T cells.

The second study examined whether it was low levels of vitamin D that is linked to multiple sclerosis (which is the widely accepted medical view) or was it low exposure to sunlight? They found that vitamin D is not associated with multiple sclerosis risk in blacks or Hispanics (but is in whites). But sun exposure is protective in all three racial/ethnic groups (blacks, Hispanics, whites). Thus it was the sunlight that was important in protecting against multiple sclerosis rather than vitamin D. Bottom line: for various beneficial health reasons, go out in sunshine frequently (20 minutes a day is fine). Remember, sunlight is the "natural source" for vitamin D (the ultraviolet light hitting our bare skin allows us to make vitamin D).

From Dec. 2016 in Science Daily: Sunlight offers surprise benefit: It energizes infection fighting T cells

Sunlight allows us to make vitamin D, credited with healthier living, but a surprise research finding could reveal another powerful benefit of getting some sun. Georgetown University Medical Center researchers have found that sunlight, through a mechanism separate than vitamin D production, energizes T cells that play a central role in human immunity.

Their findings, published today in Scientific Reports, suggest how the skin, the body's largest organ, stays alert to the many microbes that can nest there. They specifically found that low levels of blue light, found in sun rays, makes T cells move faster -- marking the first reported human cell responding to sunlight by speeding its pace.

"T cells, whether they are helper or killer, need to move to do their work, which is to get to the site of an infection and orchestrate a response," Ahern says. "This study shows that sunlight directly activates key immune cells by increasing their movement."

"We know that blue light can reach the dermis, the second layer of the skin, and that those T cells can move throughout the body," he says. ...."We found that sunlight makes hydrogen peroxide in T cells, which makes the cells move. And we know that an immune response also uses hydrogen peroxide to make T cells move to the damage," Ahern says. "This all fits together." Ahern says there is much work to do to understand the impact of these findings, but he suggests that if blue light T cell activation has only beneficial responses, it might make sense to offer patients blue light therapy to boost their immunity.

From Medscape: Is It Time to Rethink Low Vitamin D as a Contributor to MS?

The idea that vitamin D deficiency may contribute to multiple sclerosis (MS) has been well established in the literature and has, for the most part, been etched into recent neurology dogma. Yet, research by Annette Langer-Gould, MD, PhD—a clinical assistant professor at the University of Southern California's Keck School of Medicine in Los Angeles—suggests that the association might not be that simple. ....As background, the vitamin D–multiple sclerosis hypothesis originated from the observation that the prevalence of MS increases with increasing distance from the Equator, as ultraviolet radiation (UVR) from the sun becomes less intense. But this is also where more white people live.

The main result of our study is that vitamin D is not associated with MS risk in blacks or Hispanics, regardless of genotype. In contrast, sun exposure is protective in all three racial/ethnic groups.

  A recent study looking at high dose supplementation of vitamin D found that it did not prevent cardiovascular disease. This study came about because of earlier studies observing that there is a higher incidence of cardiovascular disease in persons with low vitamin D levels (as measured in their blood). But such results from observational studies need rigorous testing in studies where people are randomly assigned to groups, and that are "double-blind" (no one knows who is getting the vitamin D until the end of the study) to eliminate bias. And this is what was done in this study, with the result that monthly high doses of vitamin D3 for 3 years did not prevent cardiovascular disease (including stroke, heart attacks, hypertension, etc) - as seen in that there were no group differences between the vitamin D and placebo groups. Finding no effects are "null findings".

But note that the subjects in the study got monthly high doses, and not daily or weekly vitamin D. It is unknown whether daily dosing would have made a difference in the results. However, the vitamin D levels in the blood soon reached levels (about 51.725 ng/mL) that many view as a desirable "protective" level. So we'll see what other studies find. But these results are definitely disappointing for those wanting an easy "magic bullet" for preventing cardiovascular disease. Bottom line: focus on lifestyle (diet, exercise, not smoking, etc) for heart health. From Science Daily:

Monthly high-dose vitamin D supplementation does not prevent cardiovascular disease

Results of a large randomized trial indicate that monthly high-dose vitamin D supplementation does not prevent cardiovascular disease, according to a study published by JAMA Cardiology. Studies have reported increased incidence of cardiovascular disease (CVD) among individuals with low vitamin D status. To date, randomized clinical trials of vitamin D supplementation have not found an effect, possibly because of using too low a dose of vitamin D. Robert Scragg, M.B.B.S., Ph.D., of the University of Auckland, New Zealand, and colleagues randomly assigned adults (age 50 to 84 years) to receive oral vitamin D3 (n = 2,558; an initial dose of 200,000 IU, followed a month later by monthly doses of 100,000 IU) or placebo (n = 2,552) for a median of 3.3 years.

Of the 5,108 participants included in the primary analysis, the average age was 66 years; 25 percent were vitamin D deficient. Cardiovascular disease occurred in 303 participants (11.8 percent) in the vitamin D group and 293 participants (11.5 percent) in the placebo group. Similar results were seen for participants with vitamin D deficiency at study entry and for other outcomes such as heart attack, angina, heart failure, hypertension, and stroke.

The authors write that the results of this study do not support the use of monthly high-dose vitamin D for the prevention of CVD. "The effects of daily or weekly dosing on CVD risk require further study." [Original study.]

 I saw mention of this study in a number of places - that low vitamin D levels are linked to chronic headaches. A little too soon to know if that is really true -  the researchers in this study looked at the blood vitamin D levels of 2601 men just one time, and did not give vitamin D supplements to the men to see if this changed the frequency of migraine headaches. The researchers themselves pointed out that other studies looking at this same issue have had mixed results. And they themselves pointed out that low blood levels of vitamin D (serum 25(OH)D concentration) was associated with a markedly higher risk of frequent headache in men. Associated does not mean caused.

Yes, low vitamin D levels is linked to a number of health problems (see all vitamin D posts). But at this point I think that it's a case of "wait and see" to see if vitamin D levels have something to do with headache frequency. Perhaps other micronutrients are important, perhaps something else. Note that in the study they used below 50 nmol as the measure for low vitamin D levels. In the USA, that translates into below 20 ng/ml, which everyone agrees is too low (a deficiency). The best source of vitamin D is sunlight - which is why it's called the "sunshine vitamin". From Science Daily:

Vitamin D deficiency increases risk of chronic headache

Vitamin D deficiency may increase the risk of chronic headache, according to a new study from the University of Eastern Finland....The Kuopio Ischaemic Heart Disease Risk Factor Study, KIHD, analysed the serum vitamin D levels and occurrence of headache in approximately 2,600 men aged between 42 and 60 years in 1984-1989. In 68% of these men, the serum vitamin D level was below 50 nmol/l, which is generally considered the threshold for vitamin D deficiency. Chronic headache occurring at least on a weekly basis was reported by 250 men, and men reporting chronic headache had lower serum vitamin D levels than others.

When the study population was divided into four groups based on their serum vitamin D levels, the group with the lowest levels had over a twofold risk of chronic headache in comparison to the group with the highest levels. Chronic headache was also more frequently reported by men who were examined outside the summer months of June through September. Thanks to UVB radiation from the sun, the average serum vitamin D levels are higher during the summer months.

The study adds to the accumulating body of evidence linking a low intake of vitamin D to an increased risk of chronic diseases. Low vitamin D levels have been associated with the risk of headache also by some earlier, mainly considerably smaller studies.

 Another study finding a link with low levels of vitamin D and a health problem - this time an increased risk of bladder cancer. Vitamin D is frequently called the "sunshine vitamin" because sunlight is the best source of vitamin D (our body makes vitamin D3 from sunlight exposure on our bare skin). If you take vitamin D supplements, look for vitamin D3 (rather than D2). From Medical Xpress:

Low vitamin D levels linked to increased risk of bladder cancer

Vitamin D deficiency is associated with an increased risk of developing bladder cancer, according to a systematic review of seven studies presented today at the Society for Endocrinology annual conference in Brighton. Though further clinical studies are needed to confirm the findings, the study adds to a growing body of evidence on the importance of maintaining adequate vitamin D levels.

Vitamin D, which is produced by the body through exposure to sunshine, helps the body control calcium and phosphate levels. Vitamin D can also be obtained from food sources such as fatty fish and egg yolks. Previous studies have linked vitamin D deficiency with a host of health problems including cardiovascular disease, cognitive impairment, autoimmune conditions, and cancer.

In this work, researchers from the University of Warwick and University Hospital Coventry and Warwickshire, Coventry and the investigated the link between vitamin D and bladder cancer risk. They reviewed seven studies on the topic which ranged from having 112 to 1125 participants each. Five out of the seven studies linked low vitamin D levels to an increased risk of bladder cancer.

In a separate experiment, the researchers then looked at the cells that line the bladder, known as transitional epithelial cells, and found that these cells are able to activate and respond to vitamin D, which in turn can stimulate an immune response. According to lead author of the study Dr Rosemary Bland, this is important because the immune system may have a role in cancer prevention by identifying abnormal cells before they develop into cancer. "....our work suggests that low levels of vitamin D in the blood may prevent the cells within the bladder from stimulating an adequate response to abnormal cells," said Dr Bland. 

 A new study conducted in China found an association between low vitamin D levels and future cognitive decline in older adults. The lower the vitamin D levels at the initial screening (the baseline), the more people with cognitive decline at a 2 year follow-up. There were were no gender differences. (Another study with similar results.) Vitamin D is produced naturally in the skin when exposed to sunlight, and also found in smaller amounts in food such as fish (e.g. salmon) and eggs. Vitamin D helps maintain healthy bones and muscles, but it also plays a key part in brain function and is viewed as neuroprotective. Low levels are associated with greater risk of cardiovascular and neurodegenerative diseases.

The 1,202 participants (60 years or older) in China had their baseline vitamin D levels measured at the start of the study, and their cognitive abilities assessed over two years. What I found interesting in this study was that the vitamin D levels in the people was in general pretty low - this was without any supplementation, thus from sunlight. The researchers specified vitamin D levels (25-Cholecalciferol) in nmol/l, but in the United States values are generally specified in ng/ml. In the study the median level of vitamin D levels in the lowest quartile converted to ng/ml was 10.0 ng/ml, and in the highest quartile the median level was 26.4 ng/ml. With those low numbers, all 4 groups in the United States would be advised to supplement daily with vitamin D (specifically vitamin D3). From Journals of Gerontology: Medical Sciences:

Vitamin D Levels and the Risk of Cognitive Decline in Chinese Elderly People: the Chinese Longitudinal Healthy Longevity Survey

Vitamin D has a neuroprotective function, potentially important for the prevention of cognitive decline. Prospective studies from Western countries support an association between lower vitamin D level and future cognitive decline in elderly people.

This community-based cohort study of elderly people in China follows 1,202 cognitively intact adults aged ≥60 years for a mean duration of 2 years. Plasma vitamin D level was measured at the baseline. Cognitive state of participants was assessed using the Mini-Mental State Examination (MMSE). Cognitive impairment was defined as an MMSE score <18. Cognitive decline was defined as ≥3 points decline from baseline....Participants with low vitamin D level had an increased risk of cognitive decline. This first follow-up study of elderly people, including the oldest-old, in Asia shows that low vitamin D levels were associated with increased risk of subsequent cognitive decline and impairment.

Vitamin D is a secosteroid hormone necessary for maintaining good musculoskeletal health; its deficiency is associated with increased risks of cardiovascular and neurodegenerative diseases. Vitamin D is primarily synthesized in the skin upon exposure to sunlight; smaller amounts are obtained through dietary intake. More recently, enzymes responsible for the synthesis of its active form have been found to be distributed throughout the human brain.... This growing body of evidence suggests that vitamin D has a neuroprotective function that is potentially important for the prevention of cognitive decline. Although the importance of vitamin D cannot be disregarded, there is still no consensus on its optimal level. This is especially pertinent in the elderly people, the oldest-old in particular, as cutaneous synthesis of vitamin D decreases with age. Moreover, their impaired mobility and limited outdoor activities can further exacerbate vitamin D deficiency.

Cross-sectional studies have generally found a positive association between vitamin D status and cognitive performance in older adults. Recent prospective studies from United States and Europe support an association between diminished vitamin D status and future cognitive decline. Since cutaneous synthesis is the main source of vitamin D, there exists great variability in vitamin D levels across populations due to differences in latitude, seasons, and race/ethnicity, such as level of skin pigmentation.

Our findings were consistent with previous cohort studies showing that vitamin D status predicts cognitive decline....A notable observation in the present study is that the association of vitamin D status and cognitive decline were similar in both oldest-old and less elderly people. In this study, there was a clear association between lower 25(OH)D3 level and cognitive impairment in subjects aged ≥80....An additional difference from previous studies is that the current study indicates that the association between vitamin D and cognitive impairment is not gender specific.

The observation of temporal association between 25(OH)D3 levels and subsequent cognitive function supports the notion that vitamin D has a clinically important neuroprotective effect. A wide variety of mechanisms for this effect has been proposed and is supported by animal studies. Vitamin D has been found to modulate neuronal calcium homeostasis, cerebral process of detoxification, immunomodulation, and beta-amyloid clearance.....Further, it was unlikely that vitamin D supplementation would explain the association in this study, as 87% of the participants reported no use of vitamin supplements....In conclusion, our longitudinal study indicates that low 25(OH) D3 levels are associated with subsequent cognitive decline and cognitive impairment

 A number of recent studies looked at vitamin D and various diseases. All showed benefits of higher vitamin D levels in the blood: lower rates of cancer incidence, improved heart function in those with heart failure, lower rates of leukemia incidence, lower rates of breast cancer, and less aggressive breast and prostate cancer. However, one study found no benefits to vitamin D supplementation during pregnancy and the child's asthma risk. Older studies found low levels of vitamin D linked to higher risk of premenopausal breast cancer, and also to thicker melanomas at diagnosis (the thinner the melanoma, the better the prognosis).

Everyone agrees that sunshine is an excellent source of vitamin D, but there is still disagreement over what are the best daily vitamin D supplement dosages, or even what are optimal levels of vitamin D in the blood (measured as serum 25-hydroxyvitamin D or 25(OH)D). In 2010, the Institute of Medicine (IOM) concluded that levels lower than 12 ng/ml represented a vitamin D deficiency and recommended a target of 20 ng/ml, which could be met in most healthy adults (ages 19 to 70) with 600 International Units of vitamin D each day. Since then most researchers have argued for higher blood serum levels: most agreeing that over 30 ng/ml is best, while some advocating 50 ng/ml or more. But even what's too high (and could cause problems) is debated. Many vitamin D supporters now advocate taking 800 to 1,000 IUs of vitamin D daily (some say up to 4000 IUs daily is OK). Remember to look for vitamin D3 supplements, not D2.

This study found that higher levels of vitamin D (measured as serum 25(OH)D) are better, with 25(OH)D concentrations of at least 40 ng/ml best to reduce cancer risk (all types of cancer). From Medical Xpress: Higher levels of vitamin D correspond to lower cancer risk, researchers say

Researchers at University of California, San Diego School of Medicine report that higher levels of vitamin D - specifically serum 25-hydroxyvitamin D - are associated with a correspondingly reduced risk of cancer. The findings are published in the April 6, online issue of PLOS ONE.

Garland and his late brother, Frank, made the first connection between vitamin D deficiency and some cancers in 1980 when they noted populations at higher latitudes (with less available sunlight) were more likely to be deficient in vitamin D, which is produced by the body through exposure to sunshine, and experience higher rates of colon cancer. Subsequent studies by the Garlands and others found vitamin D links to other cancers, such as breast, lung and bladder.

The new PLOS ONE study sought to determine what blood level of vitamin D was required to effectively reduce cancer risk....The only accurate measure of vitamin D levels in a person is a blood test....Cancer incidence declined with increased 25(OH)D. Women with 25(OH)D concentrations of 40 ng/ml or greater had a 67 percent lower risk of cancer than women with levels of 20 ng/ml or less.

Garland does not identify a singular, optimum daily intake of vitamin D or the manner of intake, which may be sunlight exposure, diet and/or supplementation. He said the current study simply clarifies that reduced cancer risk becomes measurable at 40 ng/ml, with additional benefit at higher levels. "These findings support an inverse association between 25(OH)D and risk of cancer," he said, "and highlight the importance for cancer prevention of achieving a vitamin D blood serum concentration above 20 ng/ml, the concentration recommended by the IOM for bone health."

From Science Daily: Vitamin D improves heart function, study finds

A daily dose of vitamin D3 improves heart function in people with chronic heart failure, a five-year research project has found. The study involved more than 160 patients who were already being treated for their heart failure using proven treatments including beta-blockers, ACE-inhibitors and pacemakers.

Participants were asked to take vitamin D3 or a dummy (placebo) tablet for one year. Those patients who took vitamin D3 experienced an improvement in heart function which was not seen in those who took a placebo....In the 80 patients who took Vitamin D3, the heart's pumping function improved from 26% to 34%. In the others, who took placebo, there was no change in cardiac function.

Disappointing results. From Medscape: Vitamin D Disappoints: Prenatal Supplementation and Childhood Asthma

Two recent clinical trials examined maternal supplementation with vitamin D and postpregnancy offspring outcomes for asthma and wheezing....However, with respect to preventing asthma in offspring, there is no clear evidence for vitamin D supplementation in pregnant women.

From PLOS ONE: Vitamin D Deficiency at Melanoma Diagnosis Is Associated with Higher Breslow Thickness

Vitamin D deficiency at the time of melanoma diagnosis is associated with thicker tumours that are likely to have a poorer prognosis. Ensuring vitamin D levels of 50 nmol/L or higher in this population could potentially result in 18% of melanomas having Breslow thickness of <0.75 mm rather than ≥0.75 mm.

Reported in 2013. From Medical Express: Low vitamin D levels linked to high risk of premenopausal breast cancer

A prospective study led by researchers from the University of California, San Diego School of Medicine has found that low serum vitamin D levels in the months preceding diagnosis may predict a high risk of premenopausal breast cancer. The study of blood levels of 1,200 healthy women found that women whose serum vitamin D level was low during the three-month period just before diagnosis had approximately three times the risk of breast cancer as women in the highest vitamin D group. 

A 2011 meta-analysis by Garland and colleagues estimated that a serum level of 50 ng/ml is associated with 50 percent lower risk of breast cancer. While there are some variations in absorption, those who consume 4000 IU per day of vitamin D from food or a supplement normally would reach a serum level of 50 ng/ml.

 New study in the Journal of Internal Medicine  with interesting results. In the study, women were followed for 20 years, and any  deaths were put into one of 3 groups: as being from: heart disease, cancer, or other (non-heart disease and non-cancer). Swedish women followed for 20 years found that the more sunlight exposure they had, the longer the life expectancy, the less death from heart disease (cardiovascular disease) and causes other than heart disease or cancer (non-heart disease and non-cancer group), but the more skin cancer (basal cell carcinoma, squamous cell carcinoma and melanoma) they developed. Thus the main finding is of a dose-dependent relationship between sun exposure and life expectancy.

One surprising result was that nonsmokers who avoided sun exposure had a life expectancy similar to smokers in the highest sun exposure group. Those who avoided sun exposure had an increased risk of death mainly due to heart disease and "other causes" (non-cancer/non-heart disease). I wondered about other cancers in this study, and this is all they had to say in the journal article:  "Thus, women with NMSC (nonmalignant skin cancer) had a 37% higher prevalence of other internal cancers than those without NMSC and a fourfold increased prevalence of MM (malignant melanoma). The incidence of other internal cancer was not increased subsequently on NMSC diagnosis."  I now have more questions: Why didn't the incidence of other subsequent internal cancers increase once the women were diagnosed with a nonmalignant skin cancer? And how do the women with cancer in the high and low sun exposure group do after another 10 or 20 years?  I would have liked for this study to continue longer.

The researchers felt that sunshine and vitamin D had a role in these results, and suggested that we need to rethink the "avoid sunshine" advice now given to people. In other words, some sunshine is good for health. From Science Daily:

Why do sunbathers live longer than those who avoid the sun?

New research looks into the paradox that women who sunbathe are likely to live longer than those who avoid the sun, even though sunbathers are at an increased risk of developing skin cancer. An analysis of information on 29,518 Swedish women who were followed for 20 years revealed that longer life expectancy among women with active sun exposure habits was related to a decrease in heart disease and noncancer/non-heart disease deaths, causing the relative contribution of death due to cancer to increase.

Whether the positive effect of sun exposure demonstrated in this observational study is mediated by vitamin D, another mechanism related to UV radiation, or by unmeasured bias cannot be determined. Therefore, additional research is warranted. "We found smokers in the highest sun exposure group were at a similar risk as non-smokers avoiding sun exposure, indicating avoidance of sun exposure to be a risk factor of the same magnitude as smoking," said Dr. Pelle Lindqvist, lead author of the Journal of Internal Medicine study. "Guidelines being too restrictive regarding sun exposure may do more harm than good for health."

 Two recent studies link low vitamin D levels with more aggressive cancers: aggressive prostate cancer in men and more aggressive breast cancers (in mice and women). Researchers generally advise people to take 1000 to 2000 international units per day of vitamin D3 to maintain normal blood levels of of more than 30 nanograms/milliliter. The best source of vitamin D is sunlight, which is why vitamin D is frequently called the sunshine vitamin.

From Science Daily:  Low vitamin D predicts aggressive prostate cancer

A new study provides a major link between low levels of vitamin D and aggressive prostate cancer. Northwestern Medicine research showed deficient vitamin D blood levels in men can predict aggressive prostate cancer identified at the time of surgery.

"Vitamin D deficiency may predict aggressive prostate cancer as a biomarker," said lead investigator Dr. Adam Murphy, an assistant professor of urology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine urologist. "Men with dark skin, low vitamin D intake or low sun exposure should be tested for vitamin D deficiency when they are diagnosed with an elevated PSA or prostate cancer. Then a deficiency should be corrected with supplements."

Aggressive prostate cancer is defined by whether the cancer has migrated outside of the prostate and by a high Gleason score. A low Gleason score means the cancer tissue is similar to normal prostate tissue and less likely to spread; a high one means the cancer tissue is very different from normal and more likely to spread. The study was part of a larger ongoing study of 1,760 men in the Chicago area examining vitamin D and prostate cancer. The current study included 190 men, average age of 64, who underwent a radical prostatectomy to remove their prostate from 2009 to 2014.

Of that group, 87 men had aggressive prostate cancer. Those with aggressive cancer had a median level of 22.7 nanograms per milliliter of vitamin D, significantly below the normal level of more than 30 nanograms/milliliter. The average D level in Chicago during the winter is about 25 nanograms/milliliter, Murphy noted....The Institute of Medicine recommends 600 international units of D per day, but Murphy recommends Chicago residents get 1,000 to 2,000 international units per day.

From Medical Xpress:  Vitamin D deficiency contributes to spread of breast cancer in mice, study finds

Breast tumors in laboratory mice deficient in vitamin D grow faster and are more likely to metastasize than tumors in mice with adequate levels of vitamin D, according to a preliminary study by researchers at the Stanford University School of Medicine.The research highlights a direct link between circulating vitamin D levels and the expression of a gene called ID1, known to be associated with tumor growth and breast cancer metastasis.

The finding builds upon several previous studies suggesting that low levels of vitamin D not only increase a person's risk of developing breast cancer, but are also correlated with more-aggressive tumors and worse prognoses. Although the research was conducted primarily in mice and on mouse cells, the researchers found in a study of 34 breast cancer patients that levels of circulating vitamin D were inversely correlated with the expression levels of ID1 protein in their tumors, and they confirmed that a vitamin D metabolite directly controls the expression of the ID1 gene in a human breast cancer cell line.

Once ingested or made by the body, vitamin D is converted through a series of steps into its active form, calcitriol. Calcitriol binds to a protein in cells called the vitamin D receptor, which then enters the cell's nucleus to control the expression of a variety of genes, including those involved in calcium absorption and bone health.

In the new study, Williams and Aggarwal investigated whether vitamin D levels affected the metastatic ability of mouse breast cancer cells implanted into the mammary fat pad of laboratory mice. One group of 10 mice was first fed a diet lacking in the vitamin for 10 weeks; the other 10 received a normal dose in their food. Mice fed a diet deficient in vitamin D developed palpable tumors an average of seven days sooner than their peers, and after six weeks of growth those tumors were significantly larger in size than those in animals with adequate vitamin D levels.

 The following research finds a link (it doesn't establish cause) - but these interesting associations with vitamin D keep popping up. The research looked at leukemia rates in 172 countries and found that living closer to the equator (and assumed to have higher levels of vitamin D due to sunlight exposure) is linked to lower levels of leukemia. By far the best source of vitamin D is sunshine (and not food). From Medical Xpress:

Researchers link higher risk of leukemia to low sunlight and vitamin D

Epidemiologists at University of California, San Diego School of Medicine report that persons residing at higher latitudes, with lower sunlight/ultraviolet B (UVB) exposure and greater prevalence of vitamin D deficiency, are at least two times at greater risk of developing leukemia than equatorial populations.

These results suggest that much of the burden of leukemia worldwide is due to the epidemic of vitamin D deficiency we are experiencing in winter in populations distant from the equator," said Cedric Garland, DrPH, adjunct professor in the Department of Family Medicine and Public Health and member of Moores Cancer Center at UC San Diego Health. "People who live in areas with low solar ultraviolet B exposure tend to have low levels of vitamin D metabolites in their blood," Garland said. "These low levels place them at high risk of certain cancers, including leukemia."

According to the American Cancer Society, 54,270 cases and 24,450 deaths from leukemia occur in the United States alone each year. There is no known way to prevent most types of leukemia, though some types may be prevented by avoiding high doses of ionizing radiation, exposure to the chemical benzene, smoking and certain types of chemotherapy.

The UC San Diego study analyzed age-adjusted incidence rates of leukemia in 172 countries from GLOBOCAN, an international agency for research on cancer that is part of the World Health Organization, comparing that information with cloud cover data from the International Satellite Cloud Climatology Project. The study follows similar investigations by Garland and colleagues of other cancers, including breast, colon, pancreas, bladder and multiple myeloma. In each study, they found that reduced UVB radiation exposure and lower vitamin D levels were associated with higher risks of cancer.

Leukemia rates were highest in countries relatively closer to the poles, such as Australia, New Zealand, Chile, Ireland, Canada and the United States. They were lowest in countries closer to the equator, such as Bolivia, Samoa, Madagascar and Nigeria.

  Two recent studies found health problems associated with low levels of vitamin D: higher risk of stress fractures and also increased severity of IBS (Irritable Bowel Syndrome) symptoms. From Science Daily:

Low levels of vitamin D may increase risk of stress fractures in active individuals

Vitamin D plays a crucial role in ensuring appropriate bone density. Active individuals who enjoy participating in higher impact activities may need to maintain higher vitamin D levels to reduce their risk of stress fractures, report investigators in The Journal of Foot & Ankle Surgery.

The role of vitamin D in the body has recently become a subject of increasing interest owing to its many physiologic effects throughout multiple organ systems. Vitamin D is an essential nutrient that can behave as a hormone. It is obtained through diet and through the skin when exposed to the sun's rays. It is essential for bone development and remodeling to ensure appropriate bone mass density. Low levels of vitamin D can lead to osteoporosis, osteomalacia, decreased bone mineral density, and risk of acute fracture.

Investigators tested the serum concentration of 25(OH)D, which is used to determine vitamin D status, in patients with confirmed stress fractures....Using the standards recommended by the Vitamin D Council (sufficient range 40 to 80 ng/mL), more than 80% of these patients would have been classified as having insufficient or deficient vitamin D levels. According to the standards set by the Endocrine Society (sufficient range 30 to 100 ng/mL), over 50% had insufficient levels.

"Based on these findings, we recommend a serum vitamin D level of at least 40 ng/mL to protect against stress fractures, especially for active individuals who enjoy participating in higher impact activities," explained Dr. Miller. "This correlates with an earlier study of 600 female Navy recruits who were found to have a twofold greater risk of stress fractures of the tibia and fibula with a vitamin D level of less than 20 ng/mL compared with females with concentrations above 40 ng/mL.

From Science Daily: Large proportion of IBS sufferers are vitamin D deficient

A large proportion of people living with Irritable Bowel Syndrome (IBS) are vitamin D deficient, a new study has found. Researchers from the University of Sheffield discovered a significant association between a patient's vitamin D levels and the severity of their IBS symptoms, particularly the extent to which IBS affects their quality of life.

The study, which is the first of its kind, found that out of 51 IBS patients tested 82 per cent exhibited insufficient vitamin D levels....IBS is a chronic and debilitating functional disorder of the gastrointestinal (GI) tract which affects around 10-15 per cent of the western population. Little is known about why and how the condition develops, although it is known that diet and stress can make symptoms worse.