By Dr. Marc Sorenson, Sunlight Institute

Now that I have your undivided attention, let’s look at the evidence:

Sperm quality and number is superior in men with high vitamin D levels compared with men who are deficient,[i] and other research shows that female rats mated to deficient males have 73 percent fewer successful pregnancies than those mated to vitamin D-sufficient males.[ii] The ovaries and testes of rats that lack vitamin D receptors do not function properly;[iii] vitamin D deficiency profoundly reduces sperm production,[iv] but that condition is reversible when vitamin D is optimized.[v] This is an especially important fact since human sperm also contains vitamin D receptors.[vi]

Dr. Anne Clark assessed the vitamin D levels of about 800 men who were unable to produce a pregnancy in their wives.[vii] About one third had low D levels. After lifestyle changes and vitamin D supplementation, 40 percent of the men were able to impregnate their wives.

If vitamin D increases fertility, we would expect conception rates to be higher in summer than in winter – and so it is. Conception rates are highest in late summer.^{5, 4} For those who are having difficulty producing a pregnancy, conception may be as simple as a sunny vacation!

And what about sexuality? There is a direct correlation between high D levels and high testosterone levels in men.[viii] Since testosterone is the “love hormone” in both sexes, libido might be increased by sunlight exposure. Also, D supplementation in testosterone-deficient men increases testosterone by 25 percent in one year.[ix]

This has been known for decades: In 1939, Dr. Myerson measured circulating testosterone in men and exposed their various body parts to UV.[x] After five days of chest exposure, testosterone increased by 120 percent. When genitals were exposed, testosterone increased by 200 percent! Can you imagine the increase in tanning business if that information becomes well known?

[i] Bjerrum, Poul et al. Vitamin D is positively associated with sperm motility and increases intracellular calcium in human spermatozoa. Human Reproduction 2011;26:1307-1317.

[ii] Kwiecinski, G. et al. Vitamin D is necessary for reproductive functions of the male rat. J Nutr 1989;119:741-44.

[iii] Kinuta, K. et al. Vitamin D is an important factor in estrogen biosynthesis in both female and male gonads. Endocrinology 2000;141:1317-

[iv] Sood, S. et al. Effect of vitamin D deficiency on testicular function in the rat. Ann Nutr Metab 1992;36:203-8.

[v] Sood, S. et al. Effect of vitamin D repletion on testicular function in vitamin-D deficient rats. Ann Nutr Metab 1995;95-98

[vi] Corbett, S. et al. Vitamin d receptor found in human sperm. Urology 2006;68:1345-49

[vii] Clark, Anne. Fertility Society of Australia conference in Brisbane – paper presented by D. Clark – research was part of a doctoral study by University of Sydney student Laura Thomson. News.com.au Oct 19 2008

[viii] Wehr, E et al. Association of vitamin D status with serum androgen levels in men. Clin Endocrinol (Oxf) 2010;73(2):243-8

[ix] Pilz, S. et al. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res 2011;43(3):223-5

[x] Myerson, A. Influence of ultraviolet radiation on excretion of sex hormones in the male. Endocrinology 1939;25:7-12

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