The last post was about several reviews of vitamin D studies, and how when people are put randomly into different groups and then followed for a while - that the studies generally are not finding the same wonderful effects of higher levels of vitamin D in the blood that observational studies are finding - instead finding no effect or mixed results. Some issues with observational studies: the groups are self-selected, some are a one time snapshot of a person (thus one can't tell what happens over time); and can't prove cause and effect (can only say there is an association or link). [See all posts about vitamin D.]
But anyway, today's post is about some more vitamin D studies, all published in 2018. All of them find health benefits from higher blood levels of vitamin D. What is an ideal level of vitamin D varies from study to study, and some are observational - thus can only say "find an association with" in the findings. The fifth study finds beneficial effects from higher doses of vitamin D, and the participants were randomly assigned to the groups (good!). Click on links to read details. All excerpts are from Science Daily:
An epidemiological study conducted by researchers at University of California San Diego School of Medicine and Seoul National University suggests that persons deficient in vitamin D may be at much greater risk of developing diabetes. The findings are reported in the April 19, 2018 online issue of PLOS One.
For the study, the researchers identified the minimum healthy level of 25-hydroxyvitamin D in blood plasma to be 30 nanograms per milliliter. This is 10 ng/ml above the level recommended in 2010 by the Institute of Medicine, now part of The National Academies, a health advisory group to the federal government. Many groups, however, have argued for higher blood serum levels of vitamin D, as much as 50 ng/ml. The matter remains hotly debated.
"We found that participants with blood levels of 25-hydroxyvitamin D that were above 30 ng/ml had one-third of the risk of diabetes and those with levels above 50 ng/ml had one-fifth of the risk of developing diabetes," said first author Sue K. Park, MD, in the Department of Preventive Medicine at Seoul National University College of Medicine in South Korea.
Results of a study carried out in Brazil showed a strong association between vitamin D deficiency and metabolic syndrome in postmenopausal women. The Metabolic syndrome (MetS), described as a cluster of conditions that heighten the risk of heart disease, stroke and diabetes, is estimated to affect approximately 50% of the female population above the age of 50 in the United States.
Researchers at São Paulo State University's Botucatu Medical School (FMB-UNESP) detected MetS in 57.8% of the women analyzed with vitamin D insufficiency (20-29 nanograms per milliliter of blood) or deficiency (less than 20 ng/ml) and in only 39.8% of participants with sufficient vitamin D (30 ng/ml or more).
In a previous study, the UNESP researchers also analyzed the association between vitamin D deficiency and breast cancer in postmenopausal women. The survey involved 192 women aged 45-75 with a recent diagnosis of breast cancer and in amenorrhea for over 12 months. Levels of vitamin D were sufficient in 33.9% of the patients and insufficient or deficient in 66.1%. A higher proportion of those with vitamin D insufficiency or deficiency had high-grade tumors or metastatic disease.
High levels of vitamin D may be linked to a lower risk of developing cancer, including liver cancer, concludes a large study of Japanese adults published by The BMJ today. The researchers say their findings support the theory that vitamin D might help protect against some cancers. .... So an international research team, based in Japan, set out to assess whether vitamin D was associated with the risk of total and site specific cancer.
They analysed data from the Japan Public Health Center-based Prospective (JPHC) Study, involving 33,736 male and female participants aged between 40 to 69 years.... Participants were then monitored for an average of 16 years, during which time 3,301 new cases of cancer were recorded.
After adjusting for several known cancer risk factors, such as age, weight (BMI), physical activity levels, smoking, alcohol intake and dietary factors, the researchers found that a higher level of vitamin D was associated with a lower (around 20%) relative risk of overall cancer in both men and women. Higher vitamin D levels were also associated with a lower (30-50%) relative risk of liver cancer, and the association was more evident in men than in women. No association was found for lung or prostate cancer, and the authors note that none of the cancers examined showed an increased risk associated with higher vitamin D levels.
A normal intake of vitamin D can reduce the risk of death early substantially in people with cardiovascular disease, a Norwegian study shows. A study from the University of Bergen (UiB) concludes that people who have suffered from cardiovascular disease, and have a normal intake of vitamin D, reduce their risk of morality as a consequence of the disease by 30 per cent.
"We discovered that the right amount of vitamin D reduces the risk of death substantially. However, too much or too little increase the risk," says Professor Jutta Dierkes at the Department of Clinical Medicine, UiB, which lead the study. .... The study showed that it is favourable to have blood values around 42 to 100 nmol/l. If you have higher or lower values, you are at greater risk of dying from cardiovascular disease. .... Fish and cod liver oil are important sources to vitamin D during the winter, in addition to physical activities outdoors during the summer," Dierkes explains.
A randomized double-blind study (very good, because no one knew who was getting what) finding a beneficial effect from higher levels of vitamin D: High doses of vitamin D rapidly reduce arterial stiffness in overweight/obese, vitamin-deficient African-Americans
In just four months, high-doses of vitamin D reduce arterial stiffness in young, overweight/obese, vitamin-deficient, but otherwise still healthy African-Americans, researchers say. Rigid artery walls are an independent predictor of cardiovascular- related disease and death and vitamin D deficiency appears to be a contributor, says Dr. Yanbin Dong, geneticist and cardiologist at the Georgia Prevention Institute at the Medical College of Georgia at Augusta University.
So researchers looked at baseline and again 16 weeks later in 70 African-Americans ages 13-45 -- all of whom had some degree of arterial stiffness -- taking varying doses of the vitamin best known for its role in bone health. In what appears to be the first randomized trial of its kind, they found that arterial stiffness was improved by vitamin D supplementation in a dose-response manner in this population, they write in the journal PLOS ONE.
Overweight/obese blacks are at increased risk for vitamin D deficiency because darker skin absorbs less sunlight -- the skin makes vitamin D in response to sun exposure -- and fat tends to sequester vitamin D for no apparent purpose, says Dong, the study's corresponding author.
Participants taking 4,000 international units -- more than six times the daily 600 IUs the Institute of Medicine currently recommends for most adults and children -- received the most benefit, says Dr. Anas Raed, research resident in the MCG Department of Medicine and the study's first author. The dose, now considered the highest, safe upper dose of the vitamin by the Institute of Medicine, reduced arterial stiffness the most and the fastest: 10.4 percent in four months. "It significantly and rapidly reduced stiffness," Raed says. Two thousand IUs decreased stiffness by 2 percent in that timeframe. At 600 IUs, arterial stiffness actually increased slightly -- .1 percent -- and the placebo group experienced a 2.3 percent increase in arterial stiffness over the timeframe.