Vitamin D: helpful or hype-ful?

Is Vitamin D a miracle drug or a disappointment like almost all other vitamins?

Just recently there was a piece saying that Vitamin D may reduce pain. Today there was another news article saying Vitamin D may protect men against more aggressive prostate cancer. You name the condition and Vitamin D is claimed to help with it.

More generally, vitamins and supplements together are the products of an ever-growing, multi-billion dollar industry that escapes federal regulation to an astonishing degree.

As a scientist I am mostly skeptical of the power of vitamins and supplements to specifically provide, consistent medical benefit to those who take them.

This is not to say that these medical products (which escape regulation as medical products) have no effects on our cells and bodies. They absolutely can have powerful effects, but I think mostly these effects are unpredictable and just as likely to be negative as positive.

However, despite my skepticism, I take Vitamin D as a daily supplement. So you can imagine I must have what I think are good reasons for taking it if I see the vitamin and supplement industry more generally as dubious.

Why do I take it?

An important lead up question is –what is Vitamin D?

Wikipedia has a helpful entry on it, but I can give you the key points.

Vitamin D is paradoxically not a vitamin in the classical sense of the word.

Vitamin D is a hormone.

Vitamin D plays an important role in bone development as well as bone maintenance/health and Vitamin D deficiency causes a disease called osteo malacia, which in childhood form is known by the more familiar term “rickets”.

Vitamin D is only produced in our skin by sunlight.  This manner of hormone production–that is stimulation by an external factor (light in this case)–is extremely unusual and has important repercussions. For example, in theory, lack of exposure to UV light will make a person have dramatically lower levels of Vitamin D.

While Vitamin D is now found as a supplement in many food products such as milk, there are almost no foods that naturally have meaningful levels of this hormone. In fact, good natural sources of Vitamin D are some kinds of fatty fish and that’s it. 

So, now with this background in mind, what can Vitamin D actually do for us?

In the U.S. the FDA only allows Vitamin D supplement makers to claim that it reduces the risk of osteoporosis.

That’s it.

Low levels of Vitamin D are also associated with increased mortality, but the reasons remain unknown. Could it be bone fracture? Heart disease? Cancer?

Some folks believe Vitamin D reduces the risk for cardiovascular disease, but the data just aren’t out there yet to be sure.

prostate cancerI never took Vitamin D as a supplement until I was diagnosed with prostate cancer.

Part of the reason I take it is that a host of in vitro studies have convincingly demonstrated that cultured prostate cancer cells are killed or growth inhibited by Vitamin D.  Vitamin D deficiency has been hypothesized to be causal for prostate cancer, but there is no clear proof. Part of the reasoning supporting this hypothesis is an astonishingly strong correlation between latitude and prostate cancer risk. The closer to the equator that a man lives and hence the stronger his UV light exposure (and presumably the higher his serum Vitamin D levels) the lower his prostate cancer risk. See map above. Some believe the same kind of association exists for other cancers as well.

Remarkably, no large controlled studies of Vitamin D supplements (or blood levels) and prostate cancer risk have convincingly settled whether there is a connection. Many studies are published including one that just came out here, but this study like most yields unclear or conflicting results. This study suggest no association between blood levels of Vitamin D and overall prostate cancer risk, but hints at a reduced risk of death from prostate cancer in those with the highest Vitamin D levels.

More study is needed and to my knowledge there is even less data on Vitamin D and prostate cancer recurrence specifically, which is of most relevance to me as a prostate cancer survivor.

So why do I take it?

I believe that Vitamin D may prove useful for prostate cancer and this hormone appears to be one of the safest of the supplements. I also have fair skin and freckles making it a bit riskier for me to get a lot of sunlight that would stimulate natural Vitamin D production, although I do make a habit of getting some sun each day, which I also never really thought about before having cancer.  Thus, my overall sense is that the relative benefit from Vitamin D outweighs the risk. Vitamin D is a powerful pro-differentiation agent and based on all that I know about it, I have a hard time imagining how Vitamin D in non-massive doses could be harmful….still there is that risk.

Another factor to keep in mind is that taking Vitamin D as a supplement is not going to be the same as getting it naturally produced by your skin from sunlight. What differences there might be between natural Vitamin D and supplements remains unknown.

Of course before making any medical decision including what supplements to take or whether to get sunshine, you should talk to your doctor.


  1. On the subject of the dearth of empirical data, I would add a note about the overwhelming reliance on studies of Northern European populations in Vit-D studies, and the willful ignorance of seemingly obvious evolutionary impacts on populations exposed for generations to tropical vs sub-polar environments.

    • This is an excellent point and this problem extends to biomedical science more generally. The inclusion of more diverse populations of people in scientific studies is incredibly important and despite improved awareness of this issue today, it remains a serious problem.

  2. My doctor found low levels of vitamin D for me too and since I have started taking a supplement I have noticed a positive difference so I really do think it is significant. And it makes sense that more people are lacking vitamin D today with all the office jobs and time that is spent in front of the computer or tv instead of outside like our ancestors would have been.

  3. I had low Vit D levels and was told by an internist to take 2,000 IUs a day. When I discussed this with my gynecologist a few months later, she said due to my low levels, I should take 5,000 IUs a day. I’m taking them in liquid form, each drop is 1,000 IUs. I did a little research and found that some people are taking much larger doses. I live in a sunny, Southern climate, but due to a history of skin cancer in my family, I usually wear long sleeves and sunscreen all the time. I try to get more sun exposure now. It is a tough balance! Difficult to sort it all out. Thanks for sharing your thoughts.

  4. I am certain that, for some people, vitamin d supplementation is a plus. But I view all this information with a lot of skepticism, because so much of it applies to populations that evolved in Northern climates. Just out of curiosity, I recently looked at two separate articles in two different scientific magazines. One was about obesity in the world. The other one was about worldwide vitamin d supplementation. What I saw (I am not a scientist) was a strong correlation. In countries (i.e., USA and Canada) where vitamin d supplementation of milk was ubiquitous and even mandatory, obesity levels were the highest in the world. Where vitamin d was recommended but not mandatory (most of Europe), obesity was at the mid range. Where vit d supplementation was non-existent, so was obesity. Yes, I know, correlation does not imply causation, but then, the correlation in your map does not imply causation either. Also, did you know that the average weight in the entire U.S. population began to rise in the 1940’s. Guess when vitamin d supplementation became the norm. Yep, 1940’s. Also, (again, I am no scientist), ghrelin, a hunger producing hormone, is more active during daytime hours. Guess what is also more actively produced during daytime hours? The sunshine vitamin, vitamin d. Is there something wrong with adding it to our stomachs (where ghrelin is mostly produced) at any time of day or night? Who knows? But it does worry me when scientists claim that mother’s milk does not produce the amount of vitamin d needed by a newborn baby, and so they claim no baby should be allowed to leave a U.S. hospital without adequate vitamin d supplementation. In fact, a document I read of a vitamin d conference said that, in order to make vitamin d contain the amount they (the scientists) thought was adequate, the mother would have to have so much intake that it would endanger her life.!!!! How did the human race survive? Maybe vitamin d in human milk is low for a good reason, I wonder? For the record, I am currently taking part in VITAL, a study of the effects of vitamin d supplementation in people of my age group. The study includes at least 20% of individuals of races other than northern European. I am skeptical, but I also believe in good science, and the validity of thorough empirical evidence. So, I may or may not be taking it, depending on which group I’m in. Those who are interested in the subject, can look up VITAL study, Harvard and Brigham, for more information.

  5. FYI, A recent paper published by Discovery Magazine covers a review of vitamin d supplementation or moderate sun exposure for treatment of multiple sclerosis and other auto-immune diseases. Its conclusion states that “vitamin d supplementation has to date had limited benefit….Instead, sunlight and particularly UV exposure, independently of vitamin d3 production, must be responsible for the disease incidence positively linked with latitude gradients. Our goal must be to identify the UV induced molecules that are responsible for, working together with or without vitamin d3, downregulating over-zealous immune responses.”

    A free full text is available online at

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