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Vitamin D Facts You May Not Know

The Need for Vitamin D

Many people are aware that vitamin D deficiency is commonplace in America and worldwide. A recent study found that approximately 40% of Americans were deficient in vitamin D. The same study found that vitamin D deficiency is becoming more common in people younger than age 65. The hypothesis for why younger people are more prone to vitamin D deficiency is that they spend a lot on computers, gaming devices, and big-screen television. The primary source of vitamin D is sunlight converted by the body into vitamin D.

The same researchers reported that older adults are more likely to be supplementing vitamin D and, as a result, are more resistant to vitamin D deficiency. I want to point out that these studies are looking at vitamin D deficiency and not low levels or suboptimal levels of vitamin D. Therefore, the number of people with low vitamin D is thought to be about 75% of the population.

Live Longer with Vitamin D

Most people know that vitamin D deficiency predisposes people to bone loss and infection. However, good research demonstrates that low blood levels of vitamin D are associated with an increased risk of all-cause mortality (death).

Types of Vitamin D

There are two primary forms of vitamin D, including vitamin D2 (ergocalciferol) and D3 (cholecalciferol). Small amounts of vitamin D2 are found in plant/fungus-derived foods such as certain types of mushrooms. D3 is found in small quantities in animal foods such as fish liver. However, vitamin D3 is produced by the skin when exposed to sunlight (ultraviolet B radiation). The liver and kidneys can then act on both forms to make the activated form that binds with cell receptors.

Supplemental vitamin D is available in the D2 and D3 forms. There has been debate whether these two compounds have similar benefits. However, a recent review of trials found reduced cancer mortality only with D3 supplementation, not with D2 supplementation. Another recent study found that D3 supplementation was superior to D2 in elevating blood levels of 25-hydroxyvitamin D, the major circulating form of vitamin D.

Worries of Vitamin D Toxicity

Many non-nutritional doctors recommend suboptimal doses of vitamin D supplementation and warn their patients of vitamin D toxicity. However, recent research has shown that “reports of vitamin D overdose are rare in the literature.” A blood level of vitamin D is the best way to assess one’s status. A blood level that exceeds 150 ng/ml or 375 nmol/l is considered to be the beginning of the toxic range. I rarely find this is ever the case with the many thousands of patients I test who are supplementing vitamin D.


I recommend vitamin D3 as the preferred method of supplementation over vitamin D2. As I have written about in previous articles, it is best to combine D3 with K2 for long-term supplementation as K2 directs calcium to the bones. I recommend my patients useVitamin D3+K2.


Amrein, K., Scherkl, M., Hoffmann, M. et al. Vitamin D deficiency 2.0: an update on the current status worldwide. Eur J Clin Nutr 74, 1498–1513 (2020).

Durrant L, Bucca G, Hesketh A et al. Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System Revealed Through Analysis of the Blood Transcriptome. Front Immunol. 2022;13. doi:10.3389/fimmu.2022.790444

Gaksch M, Jorde R, Grimnes G, Joakimsen R, Schirmer H, Wilsgaard T, et al. Vitamin D and mortality: Individual participant data meta-analysis of standardized 25-hydroxyvitamin D in 26916 individuals from a European consortium. PLOS ONE. 2017;12:e0170791.

Parva NR, Tadepalli S, Singh P, et al. Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012). Cureus. 2018;10(6):e2741. Published 2018 Jun 5. doi:10.7759/cureus.2741

Zhang Y, Fanf F, Tang J, Jia L, Feng Y, Xu P, et al. Association Between Vitamin D Supplementation and Mortality: Systematic Review and MetaAnalysis. Br Med J (2019) 366:l4673. doi: 10.1136/bmj.l4673

About Dr. Stengler:

Dr. Mark Stengler NMD is a bestselling author in private practice in Encinitas, California at the Stengler Center for Integrative Medicine. His weekly newsletter Dr. Stengler’s Health Breakthroughs is available at