A Tortured Love of Vitamin D

Why it may never be possible to recommend that everyone take a supplement—as much as people want to believe

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Before there was Vitaminwater, there was vitamin beer. In 1936, the Joseph Schlitz Brewing Company promised that its Sunshine Vitamin D Beer would “give you the vitamin D you need for year round vigorous health.” One ad explained: “Modern living; clothing; clouds and smoke; hours spent indoors—rob us of sunshine benefits.” So, proposing to overcome the evils of modernity with yet more modernity, everyone should “drink it each day for health.”

If someone asked why you were now drinking daily, well, it’s because of the clouds and the clothing.

Certainty of the benefits of vitamin D supplements has grown murkier in the ensuing century. Except for the promise that the beer can had a “scientific lining,” Schlitz’s claims were threadbare. All that was really known at the time was that this newly discovered compound was great at preventing rickets. Presumably “prevents rickets” didn’t play well on the beer label. Sometimes morality is the enemy of commerce.

The scientific process behind the health claims was ethically fraught, too, in that it came from University of Wisconsin researchers who owned the patent on producing the compound that had recently been named “vitamin D.” The term started as a colloquialism for what chemists know as cholecalciferol and ergocalciferol, which are not structurally or functionally similar to the other compounds widely known as “vitamins.”

D is technically a pre-hormone involved in multiple metabolic processes but mainly known to affect the levels of calcium and phosphorus in our bodies. Though little was known in the 1930s about exactly how “vitamin D” worked to prevent people’s bones from warping, the biochemist who patented the process of synthesizing the compound said, “If the public should demand vitamin D in its beer, there is no reason why [we] should not provide it.”

The demanding people weren’t ready for vitamin beer, apparently, and Schlitz took it off the market two years later. Instead cow’s milk became the delivery vehicle for vitamin D supplements in the United States. A milk-fortification law was passed to combat the scourge of rickets. So arose the belief that drinking cow’s milk was necessary for strong bones. As the dairy industry made the case in government-sponsored advertising, vitamin D actually became a primary selling point for milk—the reason that many Americans believe drinking cow’s milk is necessary still today. (Even though adult cows don’t drink it.)

But in the U.K. and elsewhere, the practice of supplementing milk with vitamin D didn’t stick. Debate still rages, and it took a major step into public consciousness last week with the largest study to date on the effect of vitamin D on respiratory infections. Published in British Medical Journal (BMJ), the study is a meta-analysis of 25 controlled trials of vitamin D intake and respiratory infections. The authors argue that vitamin D fortification could reduce deaths, in addition to inordinate costs from preventable sickness that lead to missed work (and can seriously threaten the health of immune-compromised people).

On BBC’s web site, the headline was “Vitamin D Pills ‘Could Stop Colds or Flu.’” In The Guardian it was “Vitamin D ‘Proved to Cut Risk of Colds and Flu.’” There a letter to the editor from physician Jenny Goodman also declared victory, as she has been “banging on about the benefits, and indeed the necessity, of vitamin D for decades.”

In an editorial in the British Medical Journal, though, researchers Mark Bolland and Alison Avenell note that in places where widespread fortification is not common, studies like this have been “provoking passionate arguments for and against widespread supplementation.” The researchers argue that the effect was small—a reduction in risk of respiratory infections from 42 to 40 percent. “Should these results change clinical practice? Probably not,” they concluded. “The results are heterogeneous and not sufficiently applicable to the general population.”

On a similar note, the head of nutrition science at the U.K. public-health department Louis Levy told BBC, “This study does not provide sufficient evidence to support recommending vitamin D for reducing the risk of respiratory tract infections.”

Still news of the study made its to the United States, where vitamin D deficiency is still less common, and NPR said “A Bit More Vitamin D Might Help Prevent Colds And Flu.” Time went further, with  “Here's How to Avoid Catching Colds and the Flu.”

The evidence on vitamin D supplements is deeply mixed, of course. At least eight other meta-analyses in the last five years have analyzed the effects of vitamin D supplements on respiratory infections, and only three found benefits. This study was a step toward understanding if fortifying foods would benefit more people than it would potentially harm, but it does not suggest that all people should begin supplementing themselves. So the nut of it—because all of this is understandably tough to make practical, but inevitably will be put into practice one way or another—is that Vitamin D works differently in everyone depending on their levels of vitamin K, phosphate, magnesium, and other elements of diet, as well as exposure to sunlight, clothing choices, and the amount of melanin in a person’s skin (blobs of pigment that block sunlight from creating vitamin D in the body).

There is no consensus on how much vitamin D should to be consumed by “the average person” for optimal health, and I doubt there ever will be—so long as people’s diets and lifestyles vary as much as they do. If we have reached a point as a global population where we need to consider recommendations wherein all people are supposed to be taking a pre-hormone every day for the rest of their lives, there is more to interrogate about how and why that could really be necessary and sufficient.

Most of our vitamin D comes from sunlight, and that creates a huge variable for any attempt at dietary recommendations. No one who works outdoors in the tropics is likely ever going to need a vitamin D supplement. Probably almost everyone who lives in Alaska in the winter (and doesn’t constantly eat fish or drink antique cans of Sunshine Schlitz) would benefit. At the latitudes in between, the amount of melanin in a person’s skin matters a lot. For people living in the U.S., the FDA’s approach seems well worded: “If you are an older adult, have dark skin, or are exposed to insufficient ultraviolet band radiation (such as sunlight), consume extra vitamin D from vitamin D-fortified foods and/or supplements.”

The lead author of the BMJ study, Adrian Martineau at Queen Mary University of London, is an advocate of fortifying foods with vitamin D, as opposed to testing individuals and “topping up those with lowest levels.” In the meantime, he recommends that people in the U.K. take a supplement during the darker winter months. Even though people in the United States are less likely to have a clinically-defined “deficiency,” the new study might be useful to consider for people who get a lot of respiratory infections—or for whom those infections are particularly dangerous—and considered on a person-to-person basis with a physician.

So people are elaborate ecosystems that aren’t begging for blanket recommendations. But if sales of Vitaminwater are any indication, vitamin beer today could sell extremely well. Though the only clear benefit would be to the person selling it.