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When we think about super-nutrients, food sources that have multiple benefits for health and well-being, we tend to think of macro-nutrients like protein or specific compounds that have very noticeable physiological effects, like creatine monohydrate. But today, we ask you to consider a humble vitamin, Vitamin D.

Vitamin D, of course, has long been associated with support of bone density and strength. Vitamin D facilitates the absorption of calcium and phosphorus into bone mass, building strength and resilience. As such, supplementation with Vitamin D is particularly important for older people, who experience both decreases in bone density as they age and reduced levels of Vitamin D. (In fact, many researchers believe the two factors are related.)

This commonly known fact, however, is only the beginning of the story with Vitamin D. This versatile vitamin has been popping up more and more in the science news lately, most specifically in connection with immune response.

Before we get to that, though, let's consider the question of what exactly we know about Vitamin D. First of all, Vitamin D, the “sunshine vitamin,” isn’t actually a vitamin at all but a fat-soluble hormone, and the body produces it mostly by synthesizing it out of exposure to sunlight. (It’s also available through diet from a handful of food sources like oily fish, beef liver, egg yolks and some mushrooms).

Herein lies a problem. Most of us spend too much time indoors and even when we do venture out, we slather on plenty of sunblock. That’s good for avoiding skin cancer, but bad for a whole host of reasons in addition to just increased risk of bone fractures.

Vitamin D: The Versatile Vitamin

While women can help reduce the risk of osteoporosis after menopause by supplementing with Vitamin D, men also have a unique incentive to keep their Vitamin D blood levels within a healthy range. There is a significant amount of research linking low levels of Vitamin D with decreased testosterone levels in men. In fact, in a 2010 study published in the journal Hormone and Metabolic Research, healthy male subjects given 3332 iu of Vitamin D3 for a year ended up having 25.2% higher T-levels when compared to placebo (1 Sinha). That's a significant difference!

Deficits in Vitamin D can also lead to early onset of fatigue. In a study published in The Journal of Clinical Endocrinology and Metabolism, Vitamin D supplementation decreased fatigue after exercise in otherwise healthy, young vitamin D deficient subjects. According to this research (2 Pilz), the mechanism by which vitamin D promotes exercise fatigue resistance is through increasing mitochondrial function in skeletal muscle. Mitochondria are the muscle’s energy powerhouse, where an abundance of ATP (energy) is produced. Without sufficient Vitamin D, the mitochondria in muscle fibers cannot adequately generate the energy needed for efficient muscle contraction.

Vitamin D deficiency has also been linked to bouts of depression (especially Seasonal Affective Disorder or SAD). Researchers speculate that low levels of Vitamin D may affect the activity of the neurotransmitter serotonin. Finally, and most importantly for our purposes here, decreased Vitamin D blood levels appear to be associated with increased incidents of respiratory infections (cold and flu). Indeed, one review of 25 randomized controlled trials involving about 11,300 people suggests that participants who were vitamin D deficient saw a 12 percent reduced risk for respiratory infections after taking a vitamin D supplement (3 Martineau).

A study published in The American Journal Of Nutrition provided evidence that a therapeutic dose of Vitamin D resulted in a statistically significant (42%) decrease in the incidence of influenza infection (4 Urashima). Another study, published in the journal Science found that Vitamin D may play an important part in the innate antimicrobial response (5 Liu).

Vitamin D, COVID-19 and Immune Function

Of course, immune function has been uppermost in many of our minds these days, as America and the world finds itself in the grip of a COVID-19 pandemic. Perhaps inevitably, researchers have been moved to reinvestigate and reconsider the links between Vitamin D blood levels and healthy immune response. Early news on this scientific front has proven to be surprising and maybe even encouraging.

In a study conducted at Northwestern University, researchers detected a correlation between Vitamin D deficiency and COVID-19 mortality rates. The research team conducted a statistical analysis of data from hospitals and clinics across China, France, Germany, Italy, Iran, South Korea, Spain, Switzerland, the United Kingdom and the United States and found that patients from countries with high COVID-19 mortality rates, such as Italy, Spain and the UK, had lower levels of vitamin D compared to patients in countries that were not as severely affected.

Why would this be? The researchers theorize that Vitamin D may strengthen innate immunity and prevent overactive immune responses (or cytokine storms) that can result in hyperinflammatory conditions that severely damage lungs and lead to acute respiratory distress syndrome and death in patients (6 Ali Daneshkhah).

This research is very preliminary of course, and much more investigation is required. However, given the fact that Vitamin D insufficiency affects nearly half of the world's population and more than 40% of the US population, adequate support of Vitamin D blood levels would seem to be well indicated.

As mentioned earlier, getting a little exposure to sunlight is a great way to get the Vitamin D you need. In fact, as little as 15 minutes per day of direct (i.e. unsunblocked) exposure may be sufficient to provide a benefit. And then of course, there are food sources of Vitamin D.

If you're no big fan of oily fish or beef liver, a high-quality Vitamin D supplement will do the trick as well. A couple of 1000-iu softgels daily can provide satisfactory support of Vitamin D levels, and larger doses may be even better for older people. However you accomplish it, keep your levels of Vitamin D, the versatile sunshine vitamin, high for improved health and well-being!

Scientific References
1 Sinha A, Hollingsworth KG, Ball S, Cheetham T. Improving the vitamin d status of vitamin d deficient adults is associated with improved mitochondrial oxidative function in skeletal muscle. Clin Endocrinol Metab. 2013 Mar;98(3):E509-13. doi: 10.1210/jc.2012-3592. Epub 2013 Feb 7.

2 Pilz S, Frisch S, Koertke H, Kuhn J, Dreier J, Obermayer-Pietsch B, Dehr E, Zittermann A3 Dec 10. Effect of vitamin D supplementation on testosterone levels in men. Hormone and Metabolic Research, 09 Dec 2010, 43(3):223-225.

3 Adrian R Martineau, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 2017; 356.

4 Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010;91(5):1255–60.

5 Liu PT, et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science. 2006;311(5768):1770–3.

6 Ali Daneshkhah, Vasundhara Agrawal, Adam Eshein, Hariharan Subramanian, Hemant Kumar Roy, Vadim Backman. The Possible Role of Vitamin D in Suppressing Cytokine Storm and Associated Mortality in COVID-19 Patients. medRxiv, Posted April 30, 2020.



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