In Defense of Vitamin D: The Facts You Need to Know

By Gil Blander, PhD & Catherine Ward, December 21, 2021

sunlight and vitamin d

A recent New York Times Article began by stating: “There was no reason for the patients to receive vitamin D blood tests.” No reason other than perhaps their interest in taking their health into their own hands and becoming the best version of themselves possible. Or, maybe they were feeling tired and hit a plateau in their training with no idea why. Some, even, were just concerned about aging, and feeling healthy for as long as possible.

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The InsideTracker ethos is that it’s better to check your biomarkers before there is a reason to test (knowledge is power!). We believe that this is true for all of our biomarkers, but recently, the spotlight has been aimed at vitamin D by this article. The writer claims that the testing of vitamin D levels is overdone and unnecessary, and that as a result there is a false “pandemic” of vitamin D deficiency.

We at InsideTracker disagree with this entirely, and think that it is better to check if you have low vitamin D before you start seeing negative – or possibly irreversible –consequences, such as osteoporosis.


Why it's important to get your vitamin D levels tested

Contrary to what the NYT article suggests, it is very possible to have low levels of vitamin D without having an absorption issue or “bones cracking from a lack of the vitamin.” It is actually extremely common, especially for people in the northern hemisphere, to have low levels of vitamin D because the sun is only strong enough for vitamin D synthesis 6 months out of the year.1 

Low levels of vitamin D are even fairly common among InsideTracker users; who tend to be very active and health-conscious! You can see in the chart below that 10% of InsideTracker users have vitamin D levels at or below 20 ng/mL (the cutoff for insufficiency listed in the NYT article), and 39% of users have levels below 30 ng/mL (what is currently the lower, “normal” range according to clinical laboratories).

Vitamin D levels of IT usersBased on the prevalence of low values found among InsideTracker users, it would be reasonable to estimate that there would be even more people with low vitamin D levels in the general population.

The Times article based its arguments on two large papers that came out this year: one that shows a large, monthly dose of vitamin D does not affect incidence of heart disease, and another saying that vitamin D supplementation does not prevent cancer.

The study which found that vitamin D supplementation failed to prevent heart attacks2 used a monthly megadose (200,000 IU) of vitamin D as their supplementation protocol. Because of this, these results may not be applicable to the general population. Most people do not take one large dose every month; generally, users supplement every day with a lower dose. The authors acknowledge this in their conclusion and say that “the effects of daily or weekly dosing require further study.”

The other study mentioned in the article reported that supplementing with vitamin D did not reduce outcomes of cancer3. However, if you look at the levels of vitamin D in the subjects, both groups had levels of vitamin D greater than 30 ng/mL. There is a large amount of evidence showing that the lowest risk of mortality (this includes cancer) is associated with vitamin D levels greater than 30 ng/mL, and there is no difference in risk if you are over this level.4,5,6 If they had compared the outcomes of cancer in a population with deficient levels of vitamin D <30 or 20 ng/dL, the conclusion may have been different.

We don’t want to limit our consideration of vitamin D solely to cardiovascular disease and cancer, either! Vitamin D is a critical component of many other aspects of health, such as bone health7,8, muscle and athletic performance9,10, testosterone levels11,12,13,14, and sleep.15,16,17

Biomarkers 101 - Vitamin D (1)

What level of vitamin D will give me health benefits?

The question of what is the best level of vitamin D is the real crux of this debate. Do we need vitamin D levels above 30 ng/mL, or is 20 ng/mL adequate? At InsideTracker, we recommend that you have a vitamin D level greater than 32 ng/mL.

Our recommendation is based on several meta-analyses that found that people with higher levels of vitamin D (over 30 ng/mL) had a lower risk of mortality than those with lower levels. In 2012, a meta-analysis by Zitterman et al. found that the optimal range for the lowest risk of all-cause mortality was 30-35 ng/mL.6

This range was confirmed by a meta-analysis by Sempos et al. in 2013 which found the optimal range to be 29-36 ng/mL5, and then again by another paper in 2014 by Chowdhury et al. which concluded that vitamin D levels >30 ng/mL were ideal for lowering risk of mortality.4

Infographic - Vitamin D (1)

Can too much vitamin D be dangerous?

If you take excessively high supplemental doses of vitamin D for long periods of time, it can build up in your body to toxic levels. The symptoms of toxicity are a subsequent buildup of calcium in the blood (hypercalcemia), nausea, vomiting, and weakness.18

The NYT article discusses the danger of supplementation with doses of vitamin D so high that they’re dangerous, citing a page from the vitamin D council which says vitamin D toxicity can occur if “you take 40,000 IU per day for a couple of months or longer, or take a very large one-time dose.”19

Now, if you are familiar with vitamin D supplements (as most InsideTracker consumers are), you know that this is an extremely high dose! Here at InsideTracker, the highest supplemental vitamin D dose that we recommend is 5,000 IU per day, and that is only for 8 weeks – until you can get your blood tested again. We then adjust our recommendations based on the change in your blood vitamin D levels.

This issue also brings up one of the major benefits of testing through InsideTracker. Our platform explains your results, and guides you to your goals with specific recommendations tailored to your biomarker levels, your personal profile data, and your current diet and lifestyle habits. You won’t ever end up guessing the supplement dosage that’s right for you. Every one of our dosage recommendations is based on peer reviewed scientific evidence, and takes into account potential negative side effects.

A common issue we see and that we should address here, though, is that just because something is good at one dose, does not mean that more is better. We choose our supplement doses for a reason, so you should follow your InsideTracker recommendations exactly, without modifying them. If you ever have a question about a supplement or your recommendation, you can always contact us.



If you’re reading articles online arguing for or against the necessity of vitamin D supplementation, we urge you to go get tested because, in the end, as we like to say: "Blood doesn't lie!" Take your health into your own hands. You can use the InsideTracker platform to choose the best source of vitamin D that fits your lifestyle, whether that be through diet, supplementation, or simply getting some sun!






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[2] Scragg R, Stewart AW, Waayer D, Lawes CM, Toop L, Sluyter J, Murphy J, Khaw KT, Camargo CA Jr. Effect of monthly high-dose vitamin D supplementation on cardiovascular disease in the vitamin D assessment study: A randomized clinical trial. JAMA Cardiology 2017.
[3] Lappe J, Watson P, Travers-Gustafson D, Recker R, Garland C, Gorham E, Baggerly K, McDonell SL. Effect of vitamin D and calcium supplementation on cancer incidence in older women: A randomized clinical trial. JAMA 2017;317(12):1234-43.
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[15] Kim JH, Chang JH, Kim DY, Kang JW. Association between self-reported sleep duration and serum vitamin D level in elderly Korean adults. J Am Geriatr Soc 2014;62(12):2327-32.
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[18] Huang W, Shah S, Long Q, Crankshaw AKm Tangpricha V. Improvement of pain, sleep, and quality of life in chronic pain patients with vitamin D supplementation. Clin J Pain 2013;29(4):341-7.
[19] Mayo Clinic. “Vitamin D toxicity: What if you get too much?” Retrieved from:
[20] Vitamin D Council. “Am I getting too much vitamin D?” Retrieved from:

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