Vitamin D – The Optimal Level for Good Health

Do you know your vitamin D level? Is it deficient, insufficient, sufficient, or optimal? More likely than not, you’d get different answers from different doctors and even highflying ‘experts.’

In the human body, every tissue and cell have vitamin D receptors.¹ Vitamin D regulates over 2,000 genes and affects every function of our body. Its deficiency or insufficiency contributes to almost every disease, from depression to cancer, and everything in between.^1-6 In fact, vitamin D is a hormone rather than a vitamin. It was mistakenly classified as a vitamin during early 1900s.

Vitamin D in the human body is as important as engine oil for your car. Yet, vitamin D deficiency or insufficiency has been widespread. This is because only about 10% of it comes from food – no matter how well your diet is balanced, it doesn’t help much since 90% of vitamin D is from the sun interacting with your skin. But not many people get enough sun exposure since World War II, especially nowadays most of us have become office workers. Even when we’re going outside, skin cancer phobia forces us to put on layers of sun-blockers, which block the skin from making vitamin D. Bear in mind, for millions of years, our ancestors with little on the back were hunting and gathering in the open field all the time. 

Thanks to Dr. Michael Holick’s relentless effort, in the last 20 years or so, the awareness of vitamin D deficiency and insufficiency has been greatly improved. Despite the establishment’s indifference,⁷ more and more doctors test their patients’ vitamin D level, and more and more people are taking vitamin D supplements.⁸

Nevertheless, the optimal vitamin D level remains controversial and confusing. On the one hand, the Institute of Medicine (IOM) recommends 20 ng/mL as being sufficient, and doesn’t support all adults having a vitamin D level greater than 30ng/mL.^9,10 On the other hand, the U.S. Endocrine Society suggests 1500-2000 IU of vitamin D daily is needed for adults to maintain vitamin D above 30 ng/mL with preferred range of 40-60 ng/mL.¹¹ Between, the recommendation from the International Osteoporosis Foundation is to target vitamin D at 30ng/mL.¹²

The recommendation by IOM has been widely criticized for being too low – the 20 ng/mL recommendation is solely considered for bone growth, not for overall health.^6,13-17. And studies even show 20 ng/mL isn’t sufficient for bone health and pointed out the error IOM made in estimating the recommended level.^11,18,19 

Unfortunately, the IOM refuses to budge by citing the lack of evidence based on randomized controlled trials and the U-shaped mortality risk observed.²⁰

What is the U-shaped mortality risk? The widely-cited U-shaped risk is from an observational study published by Archives of Internal Medicine (now JAMA Internal Medicine) in 2008.²¹ The study found the adjusted all-cause mortality risk of 13,331 adults from the Third National Health and Nutrition Examination Survey went down as the serum vitamin D level increased, but tipped up as the vitamin D level reached about 50 ng/mL – “In our observational study we found that there was a lower risk of mortality at levels 30-49 ng/ml but that at levels > 50 ng/ml there was again a higher risk of mortality in women.”²¹

However, the adjusted U-shaped mortality risk curve is most likely flawed due to inappropriately adjusting for confounders among other methodological issues. In the study, the use of vitamin D supplementation is adjusted for as a confounder, which most likely biased the result. How many of the participants with vitamin D level greater than 50 ng/mL did not take vitamin D supplements? The serum vitamin D level is highly correlated with supplementation – this is a classic multicollinearity problem in statistics – the estimate of the effect of serum vitamin D level on mortality is unreliable in that type of analysis.

Indeed, a later meta-analysis did not find the U-shaped mortality risk – the risk keeps dropping until around 60ng/mL and becomes flat after that.²²

So, what’s the optimal level? Taken all the existing research and empirical evidence together, the optimal level for overall health is in the range of 40-60 ng/mL.¹⁷

If you’re still not sure about the optimal level and do not have the time to read the original research papers, here is a real-life reference: The traditional populations in East Africa have an average serum vitamin D concentration of 46 ng/mL despite their dark skin.²³

If you are still not convinced, the world’s foremost Vitamin D expert, Dr. Michael Holick keeps his serum vitamin D level at 50 ng/mL all year around.¹

Who is Dr. Michael Holick? You might wonder. Dr. Michael Holick, PhD, MD, is professor of Medicine, Physiology and Biophysics, Director of the General Clinical Research Unit, and Director of the Bone Health Care Clinic and Director of the Heliotherapy, Light, and Skin Research Center at Boston University. Dr. Holick first earned his PhD in biochemistry and then MD. During his graduate study, Dr. Holick was the first to identify the major circulating form of vitamin D in human blood as 25-hydroxyvitamin D3. He then identified and isolated the active form of vitamin D as 1,25-dihydroxyvitamin D3. He uncovered the mechanisms of how vitamin D is synthesized by the skin, and demonstrated the effects of aging, obesity, skin pigmentation, latitude, seasonal change, sunscreen use, and clothing on the vital cutaneous process. Dr. Holick published over 500 scientific papers.

In addition to his groundbreaking work that has advanced the understanding of vitamin D, Dr. Holick also spent decades of time to educate the public on the danger of vitamin D deficiency and insufficiency, which saved millions of people from suffering and even dying. Dr. Holick deserves the Nobel Prize.

It is a shame the medical establishment continues to indoctrinate the public with erroneous and outdated information on vitamin D which greatly increases the risk of all kinds of maladies for millions of people trusting the medical establishment.

Correcting vitamin D deficiency and insufficiency is one of the easiest things in life, so please do yourself a favor – have your serum vitamin D level tested, if not in the optimal range, get more from the sun or supplements. For more information, read Chapter 16 of Road to Health. If you really want to be an expert on Vitamin D, please read Dr. Holick’s book – The Vitamin D solution – one of the most scientific and practical books I have ever read.