This pro-hormone and essential nutrient doesn’t just regulate bone density any more!
How does Vitamin D work?
The “classical” actions of vitamin D were discovered and fleshed out between about 1918 and the late 1960s. This “vitamin” is actually a steroid pro-hormone derived from the cholesterol molecule after irradiation with ultraviolet B exposure (sunlight or lamps with the correct wavelengths) on the skin or taken orally as food or supplements.1 It must be modified a couple of times, once in the liver to 25-hydroxyvitamin D3(25(OH)D3), the storage form, and again in the kidney to make 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form.
The active form binds to the vitamin D receptor (VDR), a transcription factor that sits on DNA in cell nuclei and activates transcription of vitamin D-dependent genes. This impacts the levels of proteins made from vitamin D-dependent genes.
More recently, it’s been discovered that the brain also contains 1,25(OH)2D3, which activates pathways involved in sleep and mood.2 Pathways impacted include serotonin in and outside of the brain and melatonin production. The VDR has also been found in skeletal muscle, affecting oxidative stress, oxygen usage pathways and muscle protein breakdown.1 And it plays a role in the immune system and regulation of inflammation.3
How does this impact athletes?
Sleep
Sleep study results are mixed, partly because of the multiple sleep outcomes that can be examined and the variety of hormones involved in sleep. However, the proposed biochemical mechanism indicates that serotonin levels in the body regulate melatonin production. The pineal gland then converts serotonin into melatonin in the evening and night hours, leading to feelings of tiredness and sleepiness. This may be regulated by the daily circadian rhythms of 25(OH)D3, which peak mid-day and drop off at night.2
Mood
More than half of studies show an effect of vitamin D deficiency on depression, indicating that some portion of the population becomes depressive when deficient.3However, this is modified by the extent of the deficiency and the strength of the depression. Diagnoses of clinical depression and vitamin D deficiency show the strongest correlation. However, there is also a genetic influence.4 A study of UK Biobank data indicated a causal effect of depression on lower 25(OH)D3concentrations.
One reason for this relationship is from serotonin levels, as discussed above.2 High levels of serotonin in the brain regulate mood by regulating the hypothalamic-pituitary-adrenal axis. This regulation decreases depression by keeping normal levels of dopamine and serotonin in the adrenal cortex.
Muscle Strength and Performance
Vitamin D deficiency in skeletal muscle reduces the muscles’ ability to use oxygen optimally and regulate calcium flux within muscle cells, leading to a higher oxygen cost for exercise and weaker contractive capability.1 Vitamin D deficiency also increases oxidative stress in muscle cells, as vitamin D can function as an antioxidant. Lastly, vitamin D deficiency appears to upregulate segments of the ubiquitin protein degradation complex, increasing muscle wasting and atrophy.
Reverse Causation?
So far, discussion has been on the effects of vitamin D deficiency on sleep, mood and muscle weakness. However, reverse causation could also be at play, meaning that the sleep and mood issues, or not feeling recovered after workouts, could themselves cause vitamin D deficiency. Athletes with poor sleep, depression or tired and sore muscles may have other behaviors that cause deficiency, beginning or strengthening the symptoms. Athletes with depression may not want to train outside, thus limiting the vitamin D made in their skin. They may suffer from poor appetite or irregular eating patterns secondary to irregular sleep patterns and anxiety, limiting intake and inconsistent supplementation. Or they just might not have the energy to get outside, even if they’re feeling emotionally stable and well-rested.
Dosage and Supplement Timing
First, take your supplement at the same time every day. Because it’s a fat soluble vitamin, take it with food. The RDA for everyone from age 1 – 70 is 600 IU (15mcg)/day.5 The Endocrine Society recommends 1500-2000 IU/day. The Upper Limit, above which you should not consume or supplement, is 4000 IU/day.
Choose a supplement with third party testing! Athletes can’t afford to risk unintentional use of banned substances. There’s a blog link below to sites that list supplements tested for banned substances.
There aren’t many food sources. Fatty fish and fish oils contain vitamin D, as do fortified foods like dairy, some plant milks and orange juice.
It is very possible to make vitamin D in the skin from sunlight, as stated above. However, the ability to do this depends on the correct wavelengths of light and those don’t occur year round unless one lives in the tropics. In Chicago, we get the correct wavelengths from April to October, so at the very least, athletes should supplement from October to April. Athletes that train and compete indoors year round should consider supplementing year round.
Summary
Vitamin D is useful for improving clinical depression, sleep and muscle strength. All of these help athletes maximize their sports performance, both in training and in competing.
If you’d like to dial in your nutrient needs, contact Dr. Schubert!
Curious about working with Dr. Schubert? Read how the Magic Happens here.
Find out more on the similarities and differences between different types of milks – including vitamin D – in this blog.
Are you an athlete who’s had bariatric surgery? Read more about your needs.
Are you a vegetarian athlete? Check out your needs.
And as always, pick the supplements with Third Party Testing.
References
- Dzik KP, Kaczor JJ. Mechanisms of vitamin D on skeletal muscle function: oxidative stress, energy metabolism and anabolic state European Journal of Applied Physiology 2019;119:825–839.
- Huiberts LM, Smolders KCHJ. Effects of vitamin D on mood and sleep in the healthy population: Interpretations from the serotonergic pathway. Sleep Medicine Reviews 2021;55:101379.
- Menon V, Kar SK, Suthar N, Nebhinani N. Vitamin D and Depression: A Critical Appraisal of the Evidence and Future Directions Ind J Psych Med 2020;(42)1:11-21.
- Mulugeta A, Lumsden A, Hyppönen E. Relationship between Serum 25(OH)D and Depression: Causal Evidence from a Bi-Directional Mendelian Randomization Study. Nutrients 2021;13:109-122.
- National Institutes of Health Office of Dietary Supplements. Vitamin D, Fact Sheet for Health Professionals. Updated October 9, 2020. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed February 23, 2021.