In so-called alternative medicine (SCAM), vitamin D is often recommended for a range of indications, including cancer prevention. Observational studies did indeed suggest that low vitamin D status may be a risk factor for cancer. On the basis of such evidence, a team of researchers sought to determine if vitamin D supplementation lowers the risk of cancer and precancers.

The Vitamin D and type 2 diabetes (D2d) cancer outcomes study (D2dCA) is an ancillary study to the D2d study, which was conducted at 22 academic medical centers in the United States. Participants had prediabetes and overweight/obesity and were free of cancer for the previous 5 years. Participants were randomized to receive vitamin D3 4000 IU daily or placebo. At scheduled study visits (4 times/year), cancer and precancer events were identified by questionnaires. Clinical data were collected and adjudicated for all reported events. Cox proportional hazard models compared the hazard ratio (HR) of incident cancers and precancers between groups.

Over a median follow-up period of 2.9 years, among 2385 participants (mean age 60 years and 25-hydroxyvitamin D 28 ng/mL), there were 89 cases of cancer. The hazard ratio (HR) of incident cancer for vitamin D vs placebo was 1.07 (95% CI 0.70, 1.62). Of 241 participants with incident precancers, 239 had colorectal adenomatous polyps. The HR for colorectal polyps for vitamin D vs placebo was 0.83 (95% CI 0.64, 1.07).

The authors concluded that, in the D2d population of participants with prediabetes and overweight/obesity, not selected for vitamin D insufficiency, vitamin D supplementation did not have a significant effect on risk of incident cancer or colorectal polyps.

For some reason, the discussions about the value of vitamin D for any condition tend to be dominated by emotion rather than evidence. This is particularly true in the realm of SCAM. The trial is a significant step forward. It is rigorous and generates clear findings. Let’s hope it will contribute to a more rational debate about the value of vitamin D in cancer prevention.

8 Responses to Does vitamin D supplementation lower the risk of cancer and precancers?

  • That’s a rather daft cancer prevention study. Most cancers are present in the body for 10 – 20 years before they are large enough to be diagnosed*, so a median follow-up of 2.9 years would only show an effect if vitamin D was an effective treatment for cancer, which we know it isn’t. A much longer follow-up period is required before drawing any conclusions about the benefits or otherwise of vitamin D.**

    Personally I suspect that vitamin D must be important over and above its effects on calcium metabolism, as otherwise those living in northern latitudes wouldn’t have evolved their pale skin, with the attendant risks of sunburn and skin cancer, in order to make more of it. However, tumour prevention is probably not a strong evolutionary drive here as through most of human history people died of something else before they were old enough to get cancer.

    *By the time a cancer has reached the the size of about a gramme of tissue it has about 1,000,000,000 cells and has undergone 30 doublings, each one taking perhaps 6 – 12 months. At the time of death the tumour burden (including metastases) from most cancers is closer to 1 Kg, i.e. 1,000,000,000,000 cells, which represents another 10 doublings, though by this point it has usually become more aggressive and is doubling more quickly than before; a doubling time of 2 – 3 months is fairly typical of an uncontrolled late-stage cancer.

    **A number of cancer prevention trials have produced the unexpected result that the supplement in question has been shown to INCREASE the cancer risk, for instance a Scandinavian trial looking at vitmin C plus retinoic acid in smokers had to be stopped early due to the increased rate of lung cancer in the supplemented grouop, and more recently the SELECT trial showed that taking vitamin D increases the risk of prostate cancer.

    • Why are mainstream medics obsessed with trialling ISOLATED nutrients that we know are useful and/or essential for helping to achieve and maintain good health when they combine with other compounds in the body.
      Our immune system – for example – makes good use of Vitamin D (via the sun/food/supplements) that converts to the active form in the body known as Calcitriol, plus Vitamins K1/K2, Vitamin B Complex, Vitamin C Complex, Zinc, Selenium, Magnesium, Phosphorous, Potassium, Iodine and other supporting ‘actors’.
      I could prove to you that vitamin D prescribed to hospitalised covid patients would have little or no effect on their clinical outcomes. So what?
      As they say in the movies, move on, nothing to see here.

      • I think it’s you who might have to move on – unless you can show us that any other than the reductionist approach to research has produced anything meaningful.

      • @ Mike Grant- What is your point? Bodies need a whole array of micronutrients, vitamins, minerals- are you suggesting that supramaximal dosing of ALL these is necessary for benefits to appear??? Supplementing those with specific deficiencies is another thing entirely.

    • Some peoples have light skin colour in high latitudes because they can get away with it due to reduced sun intensity. There are lots of high latitude people that have dark skin and get away with that as well. Think Inuit, Indigenous Americans, etc. Vitamin D is not the be all and end all of health, supplement pushers notwithstanding.

  • Why did the study focus on diabetics/obese?

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