Modern health folklore and bioscience state that testosterone makes you manly and Vitamin D makes your bones strong. However, recent research indicates that these two famous biomarkers have a wide variety of functions in the body and may, in fact, impact each other’s levels. Below we document some of the key reasons why you need to stay optimized in Vitamin D and testosterone, and look at the nitty-gritty research examining the fascinating relationship between them.
D is for Design: Why you Need Vitamin D
Vitamin D is an important fat-soluble nutrient naturally found in very few foods, such as mushrooms and fatty fish (i.e. sardines, salmon, mackerel) which contain high levels of vitamin D. Other foods, such as milk, are fortified with vitamin D. The body does produce high amounts of vitamin D when skin is directly exposed to sun (i.e. not through a window), so it’s sometimes referred to as the “sunshine vitamin.” However, excess sun exposure may increase the risk of skin cancer. Because vitamin D is difficult to find in foods and prolonged sun exposure carries health risks, dieticians and doctors often prescribe supplements of varying doses.
The liver first converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol, before it is used in the body. Blood levels of this compound are the best indicator of one’s Vitamin D status.1 The kidneys then convert this substance to 1,25-dihydroxyVitamin D [1,25(OH)2D], also known as calcitriol, before it used by the body.
Vitamin D is typically associated with maintaining bone health and helping the body absorb minerals such as calcium and magnesium. 2,3 However, recent research has revealed that this biomarker also regulates cell growth and the immune system while maintaining neuromuscular and cardiovascular health. 4, 5, 6 Optimal levels of this overlooked vitamin are also crucial for athletes. Vitamin D stimulates muscle growth, increases power, and cuts unnecessary body fat. 7, 8
Despite its ever-expanding catalogue of beneficial physiological functions, vitamin D deficiency is still very prevalent. In a 2011 estimate by the Centers for Disease Control, 25% of Americans were at risk for vitamin D inadequacy (serum 25(OH)D 30-49 nmol/L) and 8% were at risk for vitamin D deficiency (serum 25(OH)D less than 30 nmol/L). 9 On the other side of the coin, excess vitamin D caused from sunlight exposure and high-dose vitamin D supplements can lead to kidney problems and nausea. 10 Some of our users, such as Laura Ingalls, experienced increased pain in joints as a result of excess vitamin D intake. When we adjust general guidelines to specific demographics and lifestyle factors, only about 14% of users have optimal levels of vitamin D. As a result, it is one of our least optimized biomarkers.
Key Takeaways: Maintaining optimal levels of vitamin D is crucial for optimal health and athletic performance. Unfortunately, vitamin D inadequacy is a public health concern and only 14% of our users have optimal levels of vitamin D.
Recommendations: It is important to regularly monitor your vitamin D status and modify your diet with appropriate foods, supplements, and lifestyle interventions to optimize your levels. Use InsideTracker to get your vitamin D data and determine which research-backed modifications, such as foods and supplements, are right for you.
Testosterone: Critical for Performance and Health
Testosterone is a crucial steroid hormone produced by both men and women. In men, testosterone levels elevate during puberty and stimulate the production of sperm and the formation of secondary sexual characteristics such as body hair and a deeper voice. In both men and women, testosterone helps increase bone strength, stimulates the development of muscle mass and strength, and improves libido and mood. Testosterone is also crucial for athletes of both genders; it helps speed tissue recovery and stimulate red blood cell blood production.
Testosterone is found in the bloodstream in one of two forms. It can be bound to the proteins albumin or sex hormone-binding globulin (SHBG), where it is known as “bound testosterone.” These proteins transport testosterone throughout the body. However, it remains biologically inactive, meaning that it does not exert its typical effects upon body cells. About 97-98% of testosterone is bound to one of these proteins. 11 The other 2-3% circulates in the blood where it can freely exert its biological effects. This portion is known as “free testosterone” (FT). While relatively small in proportion, FT is critical to maintaining optimal performance and health. The sum of bound and free testosterone is referred to as “total testosterone” (TT). All four of these testosterone biomarkers—SHBG, free testosterone, albumin, and total testosterone—are crucial indicators of health and fitness and measured in InsideTracker’s Ultimate Panel.
Knowing your testosterone levels is crucial for many reasons. Low testosterone in men is linked to infertility, irritability, and erectile dysfunction. In both men and women, low testosterone can lead to a variety of cardiovascular diseases and mental health concerns such as depression 12, 13. Testosterone is critical for performance because it facilitates anabolic, or recovery, processes 14. Low levels of free testosterone are indicative of poor recovery and can lead to poorer fitness gains and increased chance of injury. 14 Elevated testosterone in women can also lead to sexual dysfunction.
Key Takeaways: Testosterone is an important hormone with many functions in both men and women. It is important to monitor levels of total testosterone (TT), free testosterone, sex hormone-binding globulin (SHGB), and albumin to maintain optimal health and performance.
Recommendations: If your testosterone levels are too low, consider increasing your recovery time if you’re overtraining, or lifting weights if you aren’t already exercising. Also, check for possible magnesium and zinc deficiencies and increase your intake of animal proteins.
Is There a Relationship?
At InsideTracker, we’re always curious about the relationships between biomarkers. Many fitness outlets, from Anabolic Men to the Vitamin D Council, claim that “Vitamin D fixes low T.” But what is the overall picture? Here’s a focused, comprehensive assessment of the research investigating a relationship between these critical hormones.
Evidence of a Possible Connection
A reasonable amount of research suggests an association between adequate levels of vitamin D in the body, as measured by 25(OH)D, and total testosterone (TT).
In a 2012 cross-sectional study, scientists measured levels of free testosterone (FT), total testosterone (TT), and 25(OH)D in 1,362 males, primarily white health professionals over the age of 40. The researchers divided 25(OH)D by quintile and noticed a positive, independent association between concentrations of 25(OH)D and levels of TT and FT. From lowest to highest, 25(OH)D quintile TT was 18.5, 19.4, 19.6, 20.1, and 20.0 nmol/L, and FT was 97.7, 98.2, 99.2, 100.7, and 101.5 pmol/L. 15 Most importantly, the researchers noted “that the association between 25(OH)D and total and free testosterone is linear at lower levels of 25(OH)D (below approximately 75-85 nmol/L), reaching a plateau at higher levels.” 15 This suggests that the positive association between vitamin D and levels of free and total testosterone stops when vitamin D levels are optimal in the body.
Relationship between Total Testosterone and Concentration of Serum 25(OH)D
Nimptsch, Katharina, et al. "Association between plasma 25‐OH vitamin D and testosterone levels in men." Clinical Endocrinology 77.1 (2012): 106-112.
Another cross-sectional study sought to investigate the association between vitamin D and testosterone in 652 Korean men with an average age of 56.7. Researchers measured the serum concentrations of TT, FT, and vitamin D (in the form of [25(OH)D]). The subjects had a mean serum 25(OH)D of 21.23 ng/mL, mean serum TT of 4.70 ng/mL, and a mean serum FT of 2.70 ng/mL. After adjusting for demographic and lifestyle factors such as age, season, BMI, chronic disease, and alcohol use, researchers observed a positive correlation between TT, FT, and 25(OH)D. 16 Additionally, they noted that subjects with optimized levels of testosterone (>26.51 ng/mL) had, on average, 15% more vitamin D than those with suboptimal levels of testosterone. 16
Because vitamin D plays a key role in optimal athletic performance, scientists have also investigated the relationship between serum 25(OH)D levels and testosterone in young, active men. In a 2015 study, researchers performed a retrospective analysis of 312 military service members at Fort Bragg, North Carolina. Mean serum vitamin D concentrations were 29.9 ng/mL, with 52% of subjects at suboptimal levels. Scientists noted that “serum vitamin D concentrations were a significant, positive predictor of total testosterone when controlling for age and body mass index.” 17 This data suggests that highly active people—such as military personnel and athletes—may remedy low testosterone by optimizing their vitamin D levels.
Key Takeaways: Several studies in men of different lifestyle and demographic groups show a positive, direct association between vitamin D status (as measured by 25(OH)D) and levels of free and total testosterone. This association plateaus once vitamin D levels are optimized.
Recommendations: Maintaining optimal levels of vitamin D may play a role in maintaining optimal levels of testosterone.
Vitamin D and Testosterone: Not Just for Men
Scientists have also observed a direct correlation between vitamin D and testosterone in women. In a recent cross-sectional study, researchers recruited 73 healthy, non-obese women with regular menstrual cycles and no history of hormonal imbalance. After adjusting for age, body mass index, lipid levels, and other health variables, researchers observed a positive, significant correlation between serum 25(OH)D concentrations and total testosterone levels. 18 This suggests that increasing levels of vitamin D may restore healthy levels of testosterone, though more research investigating the mechanism through which this happens needs to be done.
Does Supplementation with Vitamin D Boost Testosterone?
In a 2011 randomized controlled study, researchers recruited 54 healthy men whose mean 25(OH)D levels were in the deficiency range for a year-long intervention. They divided the subjects into two groups. The first group of 23 men had an average serum 25(OH)D of 32.5 nmol/L and took a daily placebo. The second group of 31 men had an average serum 25(OH)D of 29.7 nmol/L and took a daily 3332-IU vitamin D supplement. After the trial was finished, the researchers observed a significant increase in total testosterone from 10.7 nmol/L to 13.4 nmol/L in the supplement group. 19 In contrast, there were hardly any changes in testosterone concentrations in the placebo group. 19 These findings suggest that men deficient in vitamin D who take a proper vitamin D supplement may fix low levels of low testosterone.
Key Takeaways: Subjects with suboptimal vitamin D intake showed restored optimal testosterone levels after supplementation in a randomized clinical controlled trial. While the results are promising, similar clinical trials need to be done on vitamin D-deficient men.
Recommendations: If you are proven through blood analysis to have suboptimal levels of vitamin D and testosterone, consider taking a vitamin D supplement or consuming vitamin D-rich foods to correct your deficiency. Monitor to see if supplementation affects your testosterone levels.
Some Conflicting Research on Supplementation
Not all research indicates that vitamin D supplementation optimizes testosterone levels. In a 2015 study, Dutch researchers performed a post-hoc analysis of three intervention studies investigating the effects of vitamin D supplementation on serum testosterone concentrations in vitamin D-deficient subjects. In the first study, 92 men with an average age of 63 suffering from heart failure took either a low-dose (1200-IU) vitamin D supplement or placebo for 6 weeks. In the second study, 49 nursing home residents with a median age of 82 received either a low-dose supplement of 600 IU or a placebo for 16 weeks. In the third study, 43 vitamin D-deficient male immigrants received either vitamin D (1200 IU daily) or a placebo for 16 weeks. Altogether, the studies had a total population of 184 men.
As expected, the concentrations of serum 25(OH)D increased substantially. However, there was no increase in mean testosterone concentrations at the end of any of the three studies. As a result, the researchers concluded that “In this post-hoc analysis of three small clinical trials of limited duration in men…Vitamin D supplementation was not associated with an increase in circulating testosterone concentrations.” 20 Thus, short-term, low-dose supplementation in vitamin D-deficient men does not increase testosterone in men with suboptimal levels of testosterone.
In 2012, Norwegian researchers utilized data from a longitudinal population-based study called the “Tromsø Study” to see if there is
1) A correlation between vitamin D and testosterone and
2) If supplementation with vitamin D directly increases testosterone levels
To evaluate the possible correlation, researchers noted the levels of serum 25(OH)D and total testosterone for 893 men. To assess the effect of supplementation, they observed serum 25(OH)D and testosterone in 282 vitamin D-deficient men at baseline and after 12 months of daily supplementation with 3000-6000 IU of vitamin D. After assessing the data, the authors noticed a “significant correlation between serum 25(OH)D and testosterone” in the subjects. 21 This held true even after adjustment for “age, BMI, season, presence of cardiovascular disease and diabetes, and physical activity.” 21 However, they also noted little change in testosterone levels. As a result, the authors concluded that “in subjects without significant vitamin D deficiency, there is no increase in serum testosterone after high-dose vitamin D supplementation.” 21
Key Takeaways: In large, randomized controlled studies of older men, short-term supplementation of vitamin D for subjects with sub-optimal levels of vitamin D is not shown to increase levels of testosterone. Additionally, short-term supplementation in vitamin D deficient men does increase levels of testosterone.
Recommendation: If you have sub-optimal levels of vitamin D, short-term vitamin D supplementation or eating vitamin D-rich foods is unlikely to boost your testosterone. If you already have optimal levels of vitamin D, supplementation is unlikely to increase your levels of testosterone.
Analysis: Can Vitamin D Treat Low T?
Let’s recap the evidence for the relationship between Vitamin D and testosterone:
- Several cross-sectional studies in men show an independent association between Vitamin D intake and testosterone.
- A cross-sectional study observed a correlation between Vitamin D and testosterone in women.
- One study shows an increase in levels of testosterone after providing high-dose, long-term vitamin D supplements to Vitamin D-deficient men.
- Another study observed no increase in testosterone after providing Vitamin D-deficient men with short-term Vitamin D supplementation.
- A final study observed a correlation between vitamin D and testosterone but no increase in testosterone after giving vitamin D supplements to men with optimal vitamin D.
Provided with this inconsistent evidence, what do we recommend? We encourage you to conduct your own experiment. First, use InsideTracker to monitor your Vitamin D levels and use science-based recommendations to optimize your levels. If you are low in vitamin D and testosterone, see if regularly taking the proper vitamin D supplement increases your testosterone. Remember the research: If you are already optimal in Vitamin D, supplementation is unlikely to affect your testosterone and may lead to too much Vitamin D in your body!
Putting it in Perspective
Because vitamin D and testosterone influence the body’s health and performance, it is crucial that you consistently monitor levels of these biomarkers to make sure that they are optimized. Research suggests that there is a correlation between adequate levels of vitamin D and adequate levels of testosterone. However, supplementation may only help you boost testosterone if you are already proven to be deficient in both testosterone and vitamin D.
Now we encourage you to investigate if there is a relationship between vitamin D and testosterone in YOUR body. We’ll provide you with all the data and science recommendations to optimize these biomarkers, along with 28 others related to health and performance. Click below to own your data AND health.
Men and women are affected in unique ways by sex hormones like Testosterone.
To help you understand a bit more about the role of hormones, we've created a gender-specific FREE GUIDE for you to download ...one for men, and one for women!
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List of References
1. Ross, A. Catherine, et. al. (editors) Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academies Press, 2011.
2. Horsley, Tanya, et al. Effectiveness and safety of Vitamin D in relation to bone health. US Department of Health and Human Services, Public Health Service, Agency for Healthcare Research and Quality, 2007.
3. Ross, A. Catharine, et al. "The 2011 report on dietary reference intakes for calcium and Vitamin D from the Institute of Medicine: What clinicians need to know." The Journal of Clinical Endocrinology & Metabolism 96.1 (2011): 53-58.
4. Shils, Maurice Edward, and Moshe Shike, eds. Modern Nutrition in Health and Disease. Philadelphia: Lippincott Williams & Wilkins, 2006.
5. Wang, Lu, et al. "Systematic review: Vitamin D and calcium supplementation in prevention of cardiovascular events." Annals of Internal Medicine 152.5 (2010): 315-323.
6. Hossein-Nezhad, Arash, Avrum Spira, and Michael F. Holick. "Influence of Vitamin D status and Vitamin D3 supplementation on genome wide expression of white blood cells: A randomized double-blind clinical trial." PLoS One 8.3 (2013): e58725.
7. Wyon, Matthew A., et al. "The influence of winter Vitamin D supplementation on muscle function and injury occurrence in elite ballet dancers: A controlled study." Journal of Science and Medicine in Sport 17.1 (2014): 8-12.
8.Forney, Laura A., et al. "Vitamin D Status, Body Composition, and Fitness Measures in College-Aged Students." The Journal of Strength & Conditioning Research 28.3 (2014): 814-824.
9. Looker A.C., C.L. Johnson, D.A. Lacher, et al. Vitamin D status: United States 2001–2006. NCHS data brief, no 59. Hyattsville, MD: National Center for Health Statistics, 2011.
10. Jones, Glenville. "Pharmacokinetics of Vitamin D toxicity." The American Journal of Clinical Nutrition 88.2 (2008): 582S-586S.
11. Emadi-Konjin, Pasha, Jerald Bain, and Irvin L. Bromberg. "Evaluation of an algorithm for calculation of serum 'bioavailable' testosterone (BAT)." Clinical Biochemistry 36.8 (2003): 591-596.
12. Westley, Christopher J., Richard L. Amdur, and Michael S. Irwig. "High Rates of Depression and Depressive Symptoms among Men Referred for Borderline Testosterone Levels." The Journal of Sexual Medicine (2015).
13. Wickramatilake, Chandima Madhu, Mohamed R. Mohideen, and Chitra Pathirana. "Association of metabolic syndrome with testosterone and inflammation in men." Annales d'Endocrinologie. Elsevier Masson, 2015.
14. Chung, Kyung-Jin and Khae-Hawn Kim. "Forbidden fruit for athletes, but possible divine blessing for rehabilitation: testosterone." Journal of Exercise Rehabilitation 11.1 (2015): 2.
15. Nimptsch, Katharina, et al. "Association between plasma 25‐OH Vitamin D and testosterone levels in men." Clinical Endocrinology 77.1 (2012): 106-112.
16.Tak, Young Jin, et al. "Serum 25-hydroxyVitamin D levels and testosterone deficiency in middle-aged Korean men: a cross-sectional study." Asian Journal of Andrology 17.2 (2015): 324.
17. Wentz, Laurel, et al. "Vitamin D Correlation with Testosterone Concentration in US Army Special Operations Personnel." The FASEB Journal 29.1 Supplement (2015): 733-5.
18. Chang, Eun Mi, et al. "Association between sex steroids, ovarian reserve, and Vitamin D levels in healthy non-obese women." The Journal of Clinical Endocrinology & Metabolism 99.7 (2014): 2526-2532.
19. Pilz, S., et al. "Effect of Vitamin D supplementation on testosterone levels in men." Hormone and Metabolic Research 43.3 (2011): 223.
20. Heijboer, Annemieke C., et al. "Vitamin D supplementation and testosterone concentrations in male human subjects." Clinical endocrinology (2015).
21. Jorde, R., et al. "Supplementation with Vitamin D does not increase serum testosterone levels in healthy males." Hormone and metabolic research= Hormon-und Stoffwechselforschung= Hormones et métabolisme 45.9 (2013): 675-681.