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  Does vitamin D prevent cancer? There has been much debate over whether increasing levels of vitamin D (as measured in a person's blood) results in a lower incidence of cancer. Studies find a number of health problems linked to low levels of vitamin D (here, here, here), while studies looking at vitamin D and cancer have been "inconsistent" in their results. Some say yes - vitamin D is protective, while some say there is no effect from vitamin D supplements. Now a 4 year study (yes, yes - it's a very short length of time in which to study the onset of cancer) found no difference in the rate of cancer among two groups of postmenopausal women who received either: 2,000 IU per day of vitamin D3 and 1,500 mg per day of calcium OR an identical looking placebo. They looked for any kind of cancer occurring.

The Creighton University researchers found a difference among the women after 4 years, with the vitamin D plus calcium supplement group having fewer cancers (and a lower percentage of cancer) as compared to the placebo group, but...it did not reach statistical significance. So you could say it was due to chance. But when the researchers looked at the number of cancers from year 2 to 4, then the difference was statistically significant - that vitamin D was protective. The researchers wonder if the cancers diagnosed in year 1 were already developing before the study started. Note: The 2,000 IU per day vitamin D3 supplements in this study are considered high doses - "high dose supplementation".

The researchers point out that the women who were given vitamin D3 and calcium supplements had a 30% lower risk of cancer, even though this difference in cancer incidence rates between the 2 groups did not quite reach statistical significance. But both groups started with a fairly high vitamin D level -  an average 25-hydroxyvitamin D (25[OH]D) levels of 32.8 ng/m (which is above the average US population level). And in the supplement group it was raised to 43.9 ng/mL. Note that some researchers view vitamin D levels of 33 ng/mL  (the baseline level in both groups) as already protective against cancer.

Also, even during the study the placebo group was allowed to take their own vitamin D and calcium supplements as long as it wasn't more than the recommended amounts (800 IU per day for vitamin D and 1500 mg per day for calcium) - which makes those individuals actually a low vitamin D supplementation group rather than no supplementation, which might hide any treatment effects and so make the results for the 2 groups look similar. What is needed is a much longer follow-up, larger groups of women, and both high and low dose vitamin D supplement groups. Some studies suggest that whether a low or high dose taken has an effect on cancer incidence.

I still think this study period was way too short - to me, 5 or more years would have been more convincing, and the groups too small. Also, it was unfortunate that they were also given calcium supplements or that there wasn't a just vitamin D group. Combining vitamin D with calcium supplements just muddies the results (in my opinion), and also because calcium supplements are linked to health problems such as cardiovascular disease. So in this study can't tell what the separate effects of calcium and vitamin D are. (Note that calcium rich foods, however, are beneficial to health.)

But a big positive of the study was that the women were randomly assigned to either the vitamin D plus calcium group or the placebo group, and no one - not the women or their doctors knew who got what until the end of the study (to eliminate bias it was "double-blind"). Note The supplements used were vitamin D3 and not D2. Vitamin D can also be easily obtained by exposure to sunlight in the summer months.

Excerpts from Creighton University release about the study in Science Daily: Does Vitamin D decrease risk of cancer?

The study, funded by the National Institutes of Health, is a randomized clinical trial of the effects of vitamin D supplementation on all types of cancer combined. The four-year study included 2,303 healthy postmenopausal women 55 years and older from 31 counties in Nebraska. Participants were randomly assigned to take either 2000 international units (IU) of vitamin D3 and 1500 mg. of calcium or identical placebos daily for 4 years. The vitamin D3 dose was about three times the US government's Recommended Dietary Allowance (RDA) of 600 IU for adults through age 70, and 800 IU for those 71 and older. Women who were given vitamin D3 and calcium supplements had 30% lower risk of cancer. This difference in cancer incidence rates between groups did not quite reach statistical significance. However, in further analyses, blood levels of vitamin D, specifically 25-hydroxyvitamin D (25(OH)D), were significantly lower in women who developed cancer during the study than in those who remained healthy.

  Once again, a study finds that foods are superior to supplements (here calcium supplements). It appears that eating foods rich in calcium has protective effects against kidney stones, but taking calcium supplements may result in kidney stone growth. On the other hand, vitamin D may prevent kidney stone formation. Reviewing studies over the past few years, it seems that vitamin D (the sunshine vitamin) is the one supplement with positive effects. From Science Daily:

Calcium supplements may increase the risk of kidney stone recurrence

Calcium supplements may increase the risk of kidney stone recurrence, according to a new study.

While eating foods rich in calcium has protective effects against kidney stones, the effect of supplementation with calcium and vitamin D on the risk of kidney stone formation remains unclear. To investigate, Christopher Loftus, MD candidate (Cleveland Clinic Lerner College of Medicine) and his colleagues reviewed the 24-hour urine collections and CT imaging scans from patients at their institution who had a history of kidney stones.

They identified 6050 patients with a history of kidney stones by imaging scans, 2061 of whom had 24-hour urine collections before and after starting supplementation. A total of 1486 patients were supplemented with calcium, 417 with vitamin D only, and 158 with no supplementation.

Patients who took calcium supplements had lower total calcium and oxalate (which are components of kidney stones) in their urine while blood levels were unaffected. However, these patients also had a faster rate of kidney stone growth suggesting that the mechanism of calcium supplementation on stone formation may not be straightforward. Vitamin D supplementation also decreased urinary calcium excretion as well as stone growth, suggesting that it may help prevent the risk of stone formation.

"While taking supplemental calcium has associated positive effects, these results suggest that supplemental, as compared with dietary, calcium may worsen stone disease for patients who are known to form kidney stones," said Loftus.

Macular degeneration is a feared condition, so this study finding a link with calcium supplements and age-related macular degeneration in those 68 and older is a bit alarming. However, it shows association, not causation, because it looked at people only one time. But once again supplements are looking suspect. Another reason to stick with whole foods, especially leafy greens and fish, and don't smoke. From Medscape:

Calcium Supplementation Associated With Macular Degeneration

Individuals who take more than 800 mg of calcium daily are almost twice as likely to be diagnosed with age-related macular degeneration (AMD) as those who did not, according to the results of a new study published online April 9 in JAMA Ophthalmology.

Caitlin L. M. Kakigi, BA, from the Department of Ophthalmology, University of California, San Francisco, and colleagues evaluated 3191 participants in the 2007 to 2008 National Health and Nutrition Examination Survey (NHANES) aged 40 years and older, including 248 patients with AMD diagnosed by fundus photography. Each participant was surveyed about consumption of dietary supplements and antacids during the 30-day period preceding trial enrollment.

The researchers found the odds of an AMD diagnosis were elevated among participants who reported taking 800 mg of calcium or more daily....The association was strongest in older people, with an adjusted OR of 2.63 (95% CI, 1.52 - 4.54) for those aged 68 years and older. In fact, there was no association between AMD diagnosis and calcium intake in participants younger than 68 years. The average age of participants with AMD in this study was 67.2 years compared with 55.8 years for those without an AMD diagnosis.

Rahul Khurana, MD, a clinical spokesperson for the American Academy of Ophthalmology and a partner at Northern California Retina Vitreous Associates in Mountain View, who was not involved in the study, cautioned that it is an exploratory analysis."It shows association but not causation."