Recent studies show that scary percentages of Indians suffer from vitamin D deficiency. And many of us have been scrambling to get tests—and supplements—to protect our health. But vitamin D is one of the most hotly debated topics in the medical community. Researchers can’t even agree on what constitutes a ‘deficiency’.
Researched by: Nirmal Bhansali
Say hello to vitamin D
This is what our body produces when we are exposed to the sun. Turns out we humans have our own form of photosynthesis: “When the high-energy rays of UV light—UVB—hit your skin, they start a chain reaction that converts a compound in your skin called a sterol into a vitamin D precursor.” After undergoing various metabolic processes, this molecule becomes a kind of hormone—yeah, it’s not exactly a vitamin like the others.
Why we need it: Vitamin or not, it is necessary for the absorption of calcium and phosphorus into our bones and teeth. Without enough vitamin D, calcium “leaches out” of our bones—which results in weaker bones. That’s how kids get rickets—and adults develop osteoporosis. It also helps reduce inflammation—which can trigger a variety of serious health problems.
Where you get it: Other than sunshine, vitamin D is also found in fatty fish such as salmon and tuna. You can get it from cheese and egg yolks—or fortified foods such as milk, orange juice, and cereal.
How we discovered vitamins: By the late nineteenth century, scientists had figured out that not all diseases were caused by infection. Some like beriberi were triggered by some deficiency in a person’s diet. In 1911, Casimir Funk finally figured out that trace elements of organic compounds offer the cure or prevention of deficiency diseases. He calls them vitamines—combining “vita” (Latin for “life”) and “amine” (for amino acids, building blocks of life).
How we discovered vitamin D: Sadly, this story involves torturing puppies—but in a worthy attempt to figure out what causes rickets in children. In the glorious early days of the Industrial Revolution, kids were forced to work indoors—and the outside air was blanketed with factory pollution. As a result, their bones were often seriously deformed. In 1919, Edward Mellanby stumbled on the role of vitamin D by successfully inducing rickets in puppies—by feeding them only bread and low-fat milk. Adding vitamin B-rich food did nothing to cure the disease—but butterfat and cod liver oil did the trick.
Thus, rickets was identified as the result of deficiency. In the 1920s, Elmer McCollum identified cod liver oil as a source of vitamin D—and gave its name. And in 1928, Adolf Otto Reinhold Windaus won a Nobel Prize in 1928 for showing how the body made vitamin D from sunlight.
Fun fact: In 1936, the Joseph Schlitz Brewing Company introduced “Sunshine Vitamin D” beer—urging people to “drink it daily—for health with enjoyment.” Today, just the beer can sells for nearly $500.
FYI: Vitamin D beer is still a thing. In 2022, Corona launched Corona Sunbrew—a nonalcoholic beer fortified with the good stuff.
The rise of vitamin D
Vitamin D reached peak popularity in the noughties—when a series of studies linked it to a number of serious diseases:
Beginning around 2000, a series of research papers linked vitamin D levels that are lower, but considered normal, to multiple sclerosis and mental illness, then to cancer risk and bone health… In 2007, Dr. Holick published a paper in The New England Journal of Medicine asserting that vitamin D levels… were linked to an increased risk of cancer, autoimmune disease, diabetes, schizophrenia, depression, poor lung capacity and wheezing.
That’s a pretty long and impressive list.
The ‘cure everything’ pill: Soon the discourse went beyond just deficiency—and shifted to the “benefits” of vitamin D supplements. The likes of Dr Oz—and others paid by the vitamin D makers—called it “the No. 1 thing you need more of.” In 2019, 40% of older adults in the US were taking vitamin D supplements “because they think it’s going to prevent against fractures and falls or cancer.” It became a cure-all for all sorts of maladies: “A lot of people thought that if they were fatigued or sad or they did not feel well, they might be vitamin D deficient.”
The fall of vitamin D
The problem with these studies is that they were observational. One study, for instance, ‘observed’ people without cardiovascular disease over five years—and found that people with low vitamin D levels had a higher risk of developing heart disease. But ‘seeing’ a link isn’t the same as proving cause and effect:
Think of it this way: there's a strong link between someone's wealth and the price of their car, but that doesn't mean buying an expensive vehicle will make you rich. “Just because you see an association, that doesn't mean that, okay, if we fix the serum vitamin D level, that's going to fix the problem,” says physician Leila Kahwati…
So it could be that people who take vitamin supplements are more health conscious—and less likely to get heart disease. And those who are already in poor health probably spend less time outdoors—and therefore get less vitamin D from sunlight. But that critical distinction was buried in all the hype.
The fall from grace: In 2009, scientists began the world’s largest vitamin D trial. This was a “randomised controlled trial”—where participants receive different treatments (or a placebo)—and the effects are measured. They are considered the strongest kind of medical evidence. The results of the VITAL trials were shocking:
Not only did vitamin D not make a dent in rates of cancer or heart disease, but the trial also found that vitamin D did not prevent falls, improve cognitive function, reduce atrial fibrillation, change body composition, reduce migraine frequency, improve stroke outcomes, decrease age-related macular degeneration, reduce knee pain or even reduce the risk of bone fractures.
Another major study in 2019—ViDA—showed extra vitamin D also didn't lower diabetes risk. Others revealed zero effect on mortality rates or the risk of cancers.
The more gobsmacking bit: is the abysmal confusion over the definition of deficiency:
- In 2007, the influential Dr Michael F Holick published a paper that found patients with vitamin D in a range of 21–29 ng/ml of blood are at risk of serious disease.
- Then, in 2011—as the head of a committee for the powerful Endocrine Society—Holick declared that vitamin D levels had to be at least 30 nanograms per millilitre—to be healthy.
- We ended up with a muddled and incorrect definition—where anything under 20 ng/ml represented “deficiency,” and levels of 21 to 29 ng/ml was dubbed “insufficiency.”
- The outcome: Most people were declared vitamin D deficient.
But, but, but: There is absolutely no evidentiary support for these numbers. A 2011 analysis of all vitamin D studies—by the Institute of Medicine (IOM)—definitively established the following:
- One: Any benefit from vitamin D supplements plateaus between 12 to 16 ng/ml.
- Two: there is zero benefit to having levels of vitamin D above 20 ng/ml. So IOM set that as the upper limit.
- Key number to note: the clinical definition of Vitamin D deficiency has since been set as less than 10 ng/ml.
Yet most labs and researchers instead count anything less than 20 ng/ml as deficient—thanks to the Endocrine Society. Sometimes the number is even higher, as this Scientific American piece notes:
Much of the information put out by companies offering direct-to-consumer testing still claims that anything under 30 ng/ml is low. Athlete Blood Test, for instance, markets blood tests to active people and encourages them to aim for a level of at least 50 ng/ml. While working on this story, I had my vitamin D checked by another testing company, and the laboratory results came back with reference ranges of 30 to 100 ng/ml, implying that anything under 30 was not enough.
An India example: A lot of the research in India follows the Endocrine Society’s far more generous definition of “deficiency.” Here are some examples:
- This paper—which sums up Indian studies—shows that anywhere between 50% to 94% Indians are considered deficient in vitamin D.
- According to The Print, only 20% of the population fits the clinical definition of deficiency—less than 12 ng/ml. Around 76% falls into the spurious “insufficient” category.
- More recently, a 2022 Tata 1mg Lab study put the number Indians “deficient” in vitamin D at 76%. Yes, Tata 1mg too follows the Holick-recommended range.
Quote to note: A 2016 cover story in India Today approvingly quotes Holick on the epidemic of deficiency in India—who was in town spreading his gospel of vitamin D far and wide:
"About 70% Indians are deficient in vitamin D and another 15 per cent are insufficient. If India fails to manage its vitamin D deficiency, there are high chances that it will lead to rickets, osteoporosis, cardiovascular diseases, diabetes, cancer, infections such as tuberculosis and even depression.” When Dr Michael Holick says something, the world listens. In a way, Holick is the father of vitamin D.
As it turns out, he was also paid big bucks by the vitamin D industry—and built an entire career pushing vitamin D as a miracle cure.
The recommended daily amount of vitamin D is 400 international units (IU) for children up to 12 months of age, 600 IU for people aged 1 to 70 years, and 800 IU for people aged over 70 years. For adults with vitamin D levels below 30 ng/mL, the Endocrine Society guidelines recommend a daily intake of 1,500–2,000 IU to restore healthy vitamin D levels.
That’s a huge difference—especially if you consider the fact that anything around 16 ng/ml is considered more than fine by IOM.
The bottomline: A 2010 study established that someone living in Boston in the summer months would get enough vitamin D if they received three and eight minutes of sunlight per day—with 25% of their skin exposed. Or to put it even more plainly:
You are at risk of D deficiency only if you have no sun exposure, live above 55 degrees latitude, and do not eat vitamin D-fortified foods or fluids [like milk], About 80 to 90% of vitamin D comes from sunlight, and even 15 minutes in the midday will boost vitamin D levels to a good level.
Scientific American has the best, most recent piece summarising the research—but has a moody paywall. You can read this old New York Times piece (splainer gift link) or Vox instead. For a more nuanced take on whether you should take vit D, read this piece by a nutritionist in the Washington Post—or The Atlantic. Also in the Washington Post: an entertaining history of research into vitamin D. Times of India has the Tata 1mg study. The Conversation offers a scathing take on vitamin D deficiency as a pseudo-disease. The Print and India Today have the most on the research in India—though both take Holick’s recommendations as gospel truth.