Sunshine is more than just a pleasant passing phenomenon of ever-changing weather. It is a surprisingly vital aspect of health.

In fact, research suggests sun exposure can make you healthier, happier, and even live longer.

But for those living in higher latitudes (or those who spend a lot of time indoors), the short, cold days of winter leave you desperately sun-deprived.

It’s important to “winterize” your body against the lack of sun in order to stay in optimum health.

So how do you do this?

Vitamin D.

Geography of the Sun: Where Deficiency Begins

Vitamin D3 synthesis is catalyzed by ultraviolet radiation with a UV index above 3. The only places this happens year round are close to the equator between the 37th parallels

Anywhere above the 37 degrees from the equator receives insufficient UV radiation from October all the way to March!

For the United States, this means that anyone above the southern border of Utah, Colorado, Kansas, or Virginia is vitamin D deficient for almost half the year.

And the further north you go, the worse it gets.

So why does this matter?

Vitamin D: What You Need To Know

Vitamin D is not actually a vitamin at all.

It is a hormone.

A vitamin is a necessary micronutrient that your body cannot synthesize and must be obtained through diet. While certain foods do contain this hormone, most of your vitamin D3 is made by your skin after exposure to sunlight.

UV-B light is absorbed by the skin, which induces something called “photolysis”, a multi-step process that transforms cholesterol stored in the skin cells into vitamin D3.

Once it is in circulation, like most hormones, it is involved in an shockingly wide array of biological processes.

It modulates the expression of at least 291 genes, and that's just what scientists have discovered so far. Some estimates are upwards of 2000. There are over 74,000 published, peer reviewed scientific articles on vitamin D3 and more are published every day.

The more we learn, the more we realize how important vitamin D (and regular exposure to sunlight) is to our health.

So What Exactly Does It Do?

With so many processes affected by this hormone, it has countless health benefits, but the most important come down to 5 basic categories:

• Immune Health
• Improved Mood
• Bone Health
• Cardiovascular Health
• Athletic Performance

Immune Health Higher levels of vitamin D are correlated with lower incidences of all kinds of sickness, particularly upper respiratory infections like cold and flu [1,2]. Even more compelling, it is associated with lower risk of many forms of cancer, including colon, prostate, pancreatic, ovarian, and breast cancer [3-6].

Mood Vitamin D levels show a very significant relationship to symptoms of depression. This is reflected in the appropriately named S.A.D., seasonal affective disorder, where a person experiences transient symptoms of depression over the winter months. Vitamin D supplementation has been shown to reduce depressive symptoms in a number of clinical studies [7,8], but it is important to note that depression describes a symptom, not a specific cause. In many cases, vitamin D may have no effect on these symptoms.

Bone Health One of the most powerful effects of vitamin D, especially in older populations, is in regards to bone health. Osteoblasts, the cells that secrete the matrix of bone formation, have high levels of vitamin D receptors. These activate their bone-building behaviors and promote the mineralization of bone tissue [9]. If we zoom out from the cellular level to what this actually means for real people, we find that higher levels of vitamin D levels are correlated with fewer bone fractures in all age groups [10,11] and vitamin D supplementation actually resulted in fewer falls among the elderly. There is also a potent synergistic interaction with vitamin K, another essential vitamin that improves bone health.

Cardiovascular Health In many studies, vitamin D supplementation was shown to decrease the risk of many kinds of cardiovascular disease [12], including heart disease and atherosclerosis as well as improving blood flow [13]. Like bone health, it appears to have an interaction with vitamin K.

Athletic Performance One of the most unexpected benefits of vitamin D is in athletic performance. It is curious because the levels of vitamin D receptors in muscle tissue are relatively low. Despite this, studies in rats and in muscle tissue showed improved muscle recovery using vitamin D. [14]

Special Note For the Men As we discovered above, vitamin D is a cholesterol-derived hormone, converted from cholesterol stored in your skin cells. Most of your body's hormone systems are interrelated and affect each other. Progesterone, for example, lowers the synthesis of testosterone.

What's interesting about vitamin D, however, is that it actually promotes testosterone production in men, making it one of the easiest, most reliable means of boosting your own testosterone levels. [15]

How Much Do You Really Need?

The FDA's recommended dose of 400-800 IU per day is much, much too low for a normal adult.

How much you really need depends a lot on your own baseline levels. However, due to indoor lifestyles and the ubiquitous proliferation of UV-blocking sunscreen, it is estimated that 40% of the population is vitamin D deficient.

Most successful clinical studies of Vitamin D3 use doses between 1000 and 5000 IU. The upper safety limit for Vitamin D is estimated to be somewhere around 10,000 IU, so we recommend a dose of 5000 IU to ensure optimal levels of this important hormone.

Where to Get it?

In the summer months, the easiest and cheapest source is, of course, the sun. But in the depths of winter when we are largely indoors and covered head-to-toe, it is important to supplement in order to keep your body and mind in optimal health.

Vitamin D can also be found in certain food like eggs, fish, red meat, and dairy.

For most people, however, supplementation is highly recommended. Look for high-quality brands that you can trust with at least a 2000 IU of Vitamin D3. That is the minimum you need to meet your daily requirements.

References:

1. Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. (2010)
2. Aloia JF, Li-Ng M. Re: epidemic influenza and vitamin D. Epidemiol Infect. (2007)
3. Gorham ED, et al. Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis. Am J Prev Med. (2007)
4. Skinner HG, et al. Vitamin D intake and the risk for pancreatic cancer in two cohort studies. Cancer Epidemiol Biomarkers Prev. (2006)
5. Garland CF, et al. Vitamin D and prevention of breast cancer: pooled analysis. J Steroid Biochem Mol Biol. (2007)
6. Högberg G, et al. Depressed adolescents in a case-series were low in vitamin D and depression was ameliorated by vitamin D supplementation. Acta Paediatr. (2012)
7. Sepehrmanesh Z, et al. Vitamin D Supplementation Affects the Beck Depression Inventory, Insulin Resistance, and Biomarkers of Oxidative Stress in Patients with Major Depressive Disorder: A Randomized, Controlled Clinical Trial. J Nutr. (2016)
8. Matsumoto T, et al. Stimulation by 1,25-dihydroxyvitamin D3 of in vitro mineralization induced by osteoblast-like MC3T3-E1 cells. Bone. (1991)
9. Ruohola JP, et al. Association between serum 25(OH)D concentrations and bone stress fractures in Finnish young men. J Bone Miner Res. (2006)
10. Ruohola JP, et al. Association between serum 25(OH)D concentrations and bone stress fractures in Finnish young men. J Bone Miner Res. (2006)
11. Wang TJ, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation. (2008)
12. Al Mheid I, et al. Vitamin D status is associated with arterial stiffness and vascular dysfunction in healthy humans. J Am Coll Cardiol. (2011)
13. Owens DJ, et al. A systems-based investigation into vitamin D and skeletal muscle repair, regeneration, and hypertrophy. Am J Physiol Endocrinol Metab. (2015)
14. Owens DJ, et al. A systems-based investigation into vitamin D and skeletal muscle repair, regeneration, and hypertrophy. Am J Physiol Endocrinol Metab. (2015)
15. Wehr E, et al. Association of vitamin D status with serum androgen levels in men. Clin Endocrinol (Oxf). (2010)