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Vitamin D supplements: Two research reviews find no reliable evidence of health benefits

Vitamin D supplements
None of the studies offer “highly convincing evidence of a clear role of vitamin D with highly significant results” for any health outcome, including those related to bone health.

Two more reviews of vitamin D studies were published on Tuesday in BMJ (formerly the British Medical Journal). Both came to similar conclusions: No studies to date have provided good, reliable evidence that vitamin D supplements are beneficial to health.

As I’ve said here before, I’m not sure any examination of the evidence will deter Americans from spending an estimated $600 million on vitamin D supplements every year — especially here in Minnesota, where many people seem to have bought into the overhyped notion that our northern latitude keeps us from getting sufficient vitamin D from the sun.

But I’ll keep reporting on the evidence, nevertheless.

Study No. 1

For the first study, a team of European and U.S. researchers conducted an “umbrella” review of data from more than 180 vitamin-D-related studies previously analyzed in other review articles and meta-analyses. Some of the studies had investigated whether there was a connection between disease and blood levels of vitamin D. Others had tried to determine if the taking of vitamin D supplements improves health outcomes.

The studies had linked vitamin D levels to an astounding 137 different health outcomes, including those related to heart disease, cancer, autoimmune disorders, infectious diseases and osteoporosis.

Only 10 studies, however, had been tested in well-designed clinical trials, and only one showed evidence of a health benefit. That study suggested that pregnant women with high levels of vitamin D circulating in their bodies in their final trimester were less likely to have a baby with a low birth weight.

The authors of the umbrella review also note that vitamin D levels have a “probable” association with tooth cavities in children and with thyroid-hormone levels in patients with kidney disease that requires dialysis.

But even those findings were ambiguous. None of the studies, the researchers conclude, offer “highly convincing evidence of a clear role of vitamin D with highly significant results” for any health outcome, including those related to bone health.

Any new vitamin-D-related research, they stress, must involve rigorous, well-designed studies.

Study No. 2

For the second study, an international team of researchers conducted a meta-analysis of data collected from 95 observational studies and clinical trials that had investigated vitamin D supplementation and the risk of death from all causes.

Fourteen of those studies (all randomized controlled trials) were deemed reliable. Together, they revealed that taking vitamin D3 supplements was associated with an 11 percent reduced risk of death, at least within the three- to seven-year follow-up periods of the studies.

But they also found a slight increase (about 4 percent) in the death rate among people taking vitamin D2 supplements.

Vitamin D2 (ergocalciferol) is found in plants, while natural sources of vitamin D3 (chlolecalciferol) primarily include sunlight and fatty fish, such as salmon and tuna. Vitamin D2 supplements are made synthetically by irradiating yeast. Supplements of vitamin D3 are also made through a synthetic process — by irradiating lanolin extracted from sheep’s wool. Other research suggests that the human body absorbs the synthetic form of vitamin D3 more efficiently than that of vitamin D2.

The authors of the meta-analysis warn that their findings regarding both forms of vitamin D must be interpreted with caution, for the 14 studies were small and involved elderly populations, who have many health conditions that might have influenced the results.

Like the first group of researchers, this second group also calls for more rigorous vitamin-D-related studies.

‘False reassurance’

Until those studies are done (one is in the works now and is projected to be completed by 2017), physicians should avoid recommending vitamin D supplements as prevention against disease unless there is a clear and diagnosable reason for it, write Paul Welsh and Naveed Sattar of the British Heart Foundation’s Glasgow Cardiovascular Research Center in an accompanying BMJ editorial.

They point out that the virtues of other supplements, specifically vitamins E, C and beta-carotene (vitamin A), were once widely recommended to patients — until they were shown in large, well-designed clinical trials to have no effect or even a harmful effect on health outcomes. Beta-carotene supplements have been found, for example, to increase the risk of lung cancer, particularly among smokers. And vitamin E supplements have been linked to an increased risk of prostate cancer.

“To improve health and prevent chronic disease,” write Welsh and Sattar, “we should stick to what is proven: encourage better lifestyles in general and target established risk factors in people at elevated risk.”

You’ll find links to the two studies and the editorial on the BMJ website.

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Comments (3)

  1. Submitted by Michael Blumfield on 04/02/2014 - 02:18 pm.

    Is it really so clear that Vitamin D supplements are a waste?

    I’m not certain I understand why you dismiss the value of supplements, Susan Perry. From the New York Times’ story on this research, there’s this paragraph:

    When the researchers looked at supplement use, they found no benefit to taking vitamin D2. But middle-aged and older adults who took another form, vitamin D3 — which is the type found in fish and dairy products and produced in response to sunlight — had an 11 percent reduction in mortality from all causes, compared to adults who did not. In the United States and Europe, it is estimated that more than two-thirds of the population is deficient in vitamin D. In their paper, Dr. Franco and his colleagues calculated that roughly 13 percent of all deaths in the United States, and 9 percent in Europe, could be attributed to low vitamin D levels.

    My physician recommends his patients take D vitamins. Mayo Clinic’s website lists several conditions that benefit from Vitamin D supplements. So why do you discourage others from using them?

  2. Submitted by Lance Groth on 04/02/2014 - 05:40 pm.

    Deficiency Avoidance

    I have to echo Mr. Blumfield’s comment.

    In my case, I take vitamin D and calcium supplements, on my doctor’s recommendation, not to gain any sort of magic extra health benefits, but to avoid deficiency. I do not drink milk, don’t like fatty fish (except a little tuna – let’s not forget that fatty fish are an excellent source of mercury…), and I avoid the sun in the warm months because I don’t like heat & humidity, and as a fair-skinned Norwegian I don’t fancy the idea of getting skin cancer either. When I go for walks in the summer, it’s early morning or evening (thus little or no UV). Needless to say, I don’t get any sun in the winter either, so at best I might get some useful sun (in terms of vit. D production) for a month or two in spring and fall.

    So, I think it’s a bit irresponsible to suggest that vit. D has no benefits, when in fact it is useful for people like me in avoiding deficiency-related problems.

    And that is what I think of supplements in general. If people expect supplements to cure diseases or give them a longer lifespan, then they’re off base. But, depending on lifestyle, they may well be useful for avoiding deficiencies. As a low-carb eater, I take a number of supplements selected to ensure that I’m getting all the basics. I don’t expect miracles, just making sure that any gaps are plugged.

    As for “sticking to what is proven”, the problem is that it’s difficult for lay people (and, in many cases, “experts” too, it seems) to know what is “proven”. Not a week goes by that the media don’t breathlessly report on the latest solitary research study that often contradicts previous studies that were trumpeted with equal vigor. Butter will kill you, eat margarine; oops, margarine is worse, go back to butter. Low-fat, high-carb is the way to eat; oops, that is not such good advice, turns out it made everyone fat, maybe dietary fat is ok (just recently, this column reported on research indicating that saturated fat is not a concern – a finding I agree with, but the point is the continual flip-flopping). Take vitamins to stay healthy; oops, no don’t, you might die sooner.

    What I would like to see is a moratorium on every research lab running to the media with the results of the latest solitary study. Stay in your labs, keep researching, and don’t report results to the lay audience until they have been replicated six ways from Sunday, all possible confounding factors accounted for, and the medical community reaches consensus that the information is solid (isn’t that the way science is supposed to work?). THEN dispense advice (and even then, be prepared for reversals at a future date – nutritionists, are you listening?). I’m sure it’s difficult to avoid seeking publicity when grant money is at stake, but all it does is confuse the public when contradictory results are trumpeted as the latest advice, and when that happens often enough, people just stop paying attention. “Fool me once…”, etc.

    And that’s my rant for today…

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