Most people already know that vitamin D is crucial for so many aspects of health. While I’ve written about vitamin D here on a number of occasions, as well as in every one of my books, I still see people either making mistakes in how they manage their vitamin D supplementation or, worse, being given flawed or downright erroneous advice by their doctors. If you have been following this blog, you know that doctors are not experts in health; they are experts in the business of healthcare—a big difference. Despite being crucial for health, most doctors have no idea on how to optimally manage vitamin D, as there are no sexy sales reps promising free dinner and an all-expensive-paid trip to Orlando in exchange for writing vitamin D prescriptions. So it falls mostly on you to get it right.

And getting it right can pay dividends in health: better dental health, improved composition of the gastrointestinal and vaginal microbiomes, reduced winter “blues” (seasonal affective disorder), better mood, improved bone health, improved muscle strength and muscle mass, enhanced immune response, and reduced insulin resistance are among the long list of benefits of this critical nutrient. The vast majority of people are deficient, given modern lifestyles that include wearing clothing over most body surface area and thereby blocking activation of vitamin D in the skin with sun exposure, living our lives mostly indoors, and the gradual loss of the ability to activate vitamin D in the skin as we age. It is a rare person who, without supplementation, has an optimal blood level of vitamin D (that I define as a level of 60-70 ng/ml, significantly higher than the “reference range” quoted by most labs).

Among the most frequent errors I see being committed in supplementing vitamin D:

  • Taking a non-oil based form—Oil-based gelcaps are widely available and inexpensive, with the oil component increasing absorption. Take a tablet or a capsule containing powder and absorption is erratic, sometimes yielding no absorption at all. You can improve absorption of powder or dried tablet forms by consuming with a fat- or oil-containing meal, but I find that even this practice yields erratic increases in blood levels. It’s so easy to obtain oil-based gelcap forms of vitamin D and there is therefore no reason to not take this form with assured absorption.
  • Taking vitamin D2 or ergocalciferol—Instead of the human form, D3 or cholecalciferol. As vitamin D has hormonal properties, humans do better with human forms of hormones. Just as human females were done a grave disservice for many years by receiving prescriptions for horse estrogens, rather than human, a practice that resulted in increased risk for various cancers, heart disease, and dementia, so taking the non-human form of vitamin D does not yield the same benefits as the human form, as it does not lead to sustained high blood levels nor does it bind to the vitamin D receptor as well as D3. Take only D3 or cholecalciferol, never D2 or ergocalciferol. By the way, many prescription forms are D2 and, in my view, should never be taken.
  • Stop vitamin D once a healthy blood level is achieved—I’ve witnessed this countless times: Someone begins with, say, 25-OH vitamin D blood level of 17 ng/ml (severe deficiency), supplements 8000 units per day of an oil-based gelcap that increases the blood level to 65 ng/ml. The doctor then says something like, “That’s a good level, so you can stop it now.” That advice is so painfully ignorant, as vitamin D blood levels are maintained only so long as supplementation is continued. Stopping vitamin D supplementation will, over about 3 months, return you to your starting level and exposed to all the phenomena associated with deficiency.
  • Assessing blood levels too soon—When you first start vitamin D, it requires nearly 3 months for the blood level to stabilize, reaching what we call “steady state.” Assessing a blood level too soon will therefore be misleading. This is also true with any dose change, up or down. Say your starting level was 15 ng/ml. You supplement 8,000 units per day in oil-based gelcap form and 3 months later your 25-OH vitamin D blood level is 48 ng/ml. You therefore increase your dose to 12,000 units per day, but mistakenly repeat the blood test 4 weeks later, yielding a level of 54 ng/ml—but you haven’t waited long enough to achieve steady state that likely would have been in our target range of 60-70 ng/ml. Wait the full 3 months with any dose change.
  • If you supplement vitamin D without vitamin K2, you will cause coronary calcification and increase cardiovascular risk—This, of course, is patent nonsense. The evidence that K2 supplementation reduces cardiovascular risk is weak and is falling apart as randomized clinical trails fail to show benefit. K2 may add to reducing osteoporotic hip and other fractures, but it so far has not proven advantageous for reducing cardiovascular risk. Vitamin D makes a major contribution to reducing cardiovascular risk, including providing enormous control over the progression of coronary artery calcium, all achieved without K2. (And a strong case can be made that K2 is really meant to be obtained through gastrointestinal microbes, an effect lost with colonic dysbiosis and small intestinal bacterial overgrowth, SIBO.)
  • “Bolus” dosing of vitamin D—This refers to prescriptions for high doses of vitamin D such as 50,000 units once per week, or 100,000 units once per month. While it required a number of clinical trials to reveal this phenomena, it has become clear that daily dosing of D3 provides great benefits, while bolus dosing provides none. Bolus dosing is speculated to redirect the high quantity of vitamin D into an alternative metabolic pathway that essentially negates all its benefits. There is certainly no benefit in bolus dosing, so daily dosing is key. (It is not clear what role upfront “loading” should play, i.e, larger doses of, say, 20,000 units per day over the first few days of supplementation to accelerate reaching steady state. This might have been important, for instance, during COVID when achieving an optimal level as soon as possible could be crucial. But it remains an unsettled question. The key is to not wait until some health catastrophe to supplement vitamin D, but start now.)
  • “My doctors says that my 25-OH vitamin level is fine at 35 ng/ml”—Once again, the doctor is relying on the flawed advice of the testing lab that obtained its “reference range” by testing, say, 100 volunteers who wear clothes, mostly work indoors, and included older folks who do not produce vitamin D effectively upon sun exposure. In short, reference ranges are obtained by assessing a diseased population, not a vitamin D-replete population. So instead I ask, “At what level of 25-OH vitamin D do all of its unhealthy consequences (e.g., increased parathyroid hormone, PTH, levels; population risk for various cancers; measures of insulin resistance) maximally recede? That occurs above 50 ng/ml, so for an extra “cushion” of benefit we aim for 60-70 ng/ml, a level that has also never been associated with any measure of toxicity.
  • “My doctors says that 400 units of vitamin D per day is adequate”—Come on: you’re kidding, right? Ask your doctor about Humira, or Cymbalta, or Accutane, i.e., pharmaceuticals that he/she likely knows something about. But don’t ask about the finer points of nutrients, nutrition, or the microbiome, as it would be no better than asking your auto mechanic, perhaps worse. It shouldn’t be that way, but that is the modern American healthcare system, designed to maximize revenue, not results. Dr. John Cannell of The Vitamin D Society has a helpful rule-of-thumb: Start with a dose of 1000 units per 25 pounds body weight. Someone who weighs 150 pounds, for example, could begin with a starting dose of 6000 units per day. Adjust dose in future, as there are other factors determining blood level beyond body weight (genetics, skin color, age, percent body fat, etc.), based on 25-OH vitamin D levels.
  • “I get plenty of sun, so I don’t need vitamin D.”—The majority of people living in tropical or sub-tropical latitudes such as Hawaii and southern Florida are deficient, if achieving a 25-OH vitamin D blood level of 60-70 ng/l is your goal. Also factor in the declining ability to activate vitamin D in the skin with sun exposure as we age. During my cardiology practice days in Wisconsin, snowbirds would return from Florida or Phoenix in March sporting dark leather tans and small tan lines. “Don’t test my vitamin D doc, just look at me!” I’d test them and levels of 17 or thereabouts were the rule.

It’s really so easy: Supplement every day with an oil-based supplement form of D3, have a blood test of 25-OH vitamin D run occasionally but never sooner than 3 months after starting or with any change in dose, and aim for an optimal blood level associated with multiple measures of health. There may be more lessons to learn about vitamin D, but know that you have access to a spectacularly beneficial nutrient already, but it’s best if you get it right given what is already known.