Vitamin D: No cure-all for older women

BROWN (US) — Postmenopausal women receive no additional mortality benefit from vitamin D after controlling for health risk factors such as abdominal obesity, a new study finds.

The research, consistent with advice issued last fall by the Institute of Medicine, found no evidence linking vitamin D to the prevention of cancer, cardiovascular disease, or other causes of death after controlling for health factors like abdominal obesity.

“What we have is clinical trial evidence that for the most part vitamin D doesn’t seem to be helpful for conditions where people thought it might,” says Charles Eaton, professor of family medicine and of epidemiology at Brown University.

“The best we can tell is that there isn’t an association. Once we took into account these other factors, high levels didn’t provide a benefit and low levels didn’t put you at risk.”

In the study, published online Oct. 26 in the American Journal of Clinical Nutrition, Eaton led an analysis of data from 2,429 postmenopausal women aged 50 to 79 who participated in the broad-based Women’s Health Initiative study, that tracked blood levels of vitamin D in the women and their mortality over a 10-year period. They not only looked at death from all causes but also focused on cancer and cardiovascular disease.

In all, 225 of the women died, including 79 from cardiovascular disease and 62 from cancer.

The researchers expected to find some protective effect against such mortality from vitamin D, and at first glance—controlling only for age, ethnicity, and whether women took part in a calcium and vitamin D supplement trial—that’s what the data showed.

But what was apparent in the data was that the women with the lowest levels of vitamin D also had a lot of other negative health indicators.

The team therefore controlled for several more key health factors, such as smoking, history of cardiovascular disease, history of cancer, alcohol consumption, and waist circumference. The additional controls, especially waist circumference, which is a measure of abdominal obesity, eroded the statistical significance of vitamin D’s seemingly protective effects down to nothing.

The one exception was that women with thinner waistlines (less than 35 inches) and with the lowest vitamin D levels seemed to have a greater risk of “all-cause” mortality within the 10-year analysis period. That result, however, was right on the borderline of statistical significance.

“If you are thin, this data suggest that maybe low vitamin D levels are potentially harmful and you should talk to your doctor about what to do about them,” Eaton says.

The researchers say they can only speculate about why abdominal obesity was an especially important and powerful factor to control for in their analysis. The study shows that abdominal obesity is associated with several negative health indicators that may overwhelm any modest benefit vitamin D might have. Also, fat tissue can store vitamin D, possibly meaning that women with larger waistlines are storing more of the vitamin than their blood serum levels alone would reveal.

More research into the connections between abdominal fat and the health effects of vitamin D could help resolve the question, Eaton says. He also says that a major new trial of vitamin D supplements and health called “VITAL” is getting under way and will likely inform the broader controversy about the benefits of vitamin D.

But for now, Eaton says, “there’s not enough evidence to do anything about our vitamin D levels if it’s not in regard to bone health.”

Researchers from Northwestern University, University of Pittsburgh, University of California–San Diego, University of California–Los Angeles, University of Iowa, George Washington University, University of Tennessee, University of Hawaii, and Harvard University contributed to the study.

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  1. Peter

    To quote from the paper

    “A total of 36,282 women were enrolled in the CaD–supplementation trial and were randomly assigned to
    consume either a placebo or 1000 mg calcium carbonate combined with 400 IU 25(OH)D. Women were allowed to continue their personal use of CaD as long as their vitamin intakes were not 600 IU/d (and, later, 1000 IU/d)”.

    They let the control group randomly take more than they were giving to the fortified group. They also only measured the 25(OH)D level once 10 years before. Sorry this data is useless.

  2. Peter

    Also “After adjustment for age, race-ethnicity, and participation in the CT, low vitamin D (quartiles 1 compared with 4) was associated with an increased risk of all-cause mortality (HR: 1.62; 95% CI: 1.11, 2.36) (Table 2). After adjustment for potential confounders measured at baseline, including age, race-ethnicity, CT indicator, current smokers, history of hypertension, systolic blood pressure, diabetes, history of CVD, history of fracture, waist circumference, BMI, and physical activity, risk of low vitamin D was attenuated (HR: 1.25; 95% CI: 0.80, 1.95) and lost statistical significance.”

    And vitamin d insufficiency is linked to BMI, blood pressure, CVD, diabetes and history of fracture. So if we ignore all the things that are associated with vitamin d then vitamin d has no effect.

  3. Larry

    Peter makes a great point that if you take away all the positive health results associated with vitamin D then it has no effect. Nice way to back into a non-result.

    I would add that several studies have shown that vitamin D you make is better than vitamin D you take. For example a survey of all studies relating to sunlight, vitamin D and reduction of breast, prostate, and colon cancers and lymphoma found that increased sun exposure was consistently associated with significant decreased risk of all 4 cancers while vitamin D levels were only consistently associated with a decreased risk of colon cancer. (van der Rhee 2009).

    BTW, sun exposure also appears to reduce the incidence and mortality of melanoma so it’s time to put that canard to bed. (Berwick 2004, Garland 1990 for US Navy).

    Low vitamin D is a sun deficiency not a nutritional deficiency. More studies need to focus on UV exposure which appears to be far more effective than vitamin D supplementation.

  4. Pete

    It is very unlikely that the vitamin d3 you make and that which is in supplement form behave differently as they are chemically the same. It is more likely that it is an extra effect of UV/light on the skin (something else created or an effect on the immune system) or simply that people are told to take tiny amounts of vitamin d. If the skin makes 20,000IU a day on sun exposure and you give people tablets with 400IU in them the tablets are not going to have any measurable effect simply because sun exposure will dominate.

  5. Andrea Giletti

    As Professor Holick reported in NEJM 354:2287 2006, a key message from the WHI data is that women who were Vitamin D deficient i.e. 25(OH)D <12ng, had a 253% increased risk for developing colorectal cancer during the 8 years of the study compared with women who were Vitamin D sufficient at the beginning of the study. To repeat, they had a 253% percent increased risk compared to women who were Vitamin D sufficient.
    This report was published in 2006.

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