By Alexis Lewis
Role of Nutrition in Athletic Performance
Proper nutrition and its role in affecting athletic performance has become more evident recently. Specific macro and micronutrients are better understood as to their specific functions in the body and how they influence performance under duress. An example would be the stress of athletic performance.
Vitamin-D, also known as cholecalciferol, is one of the fat-soluble vitamins that influence athletic performance. However, Vitamin-D is not necessarily a “performance enhancing” nutrient. When an individual is deficient, it can hinder athletic performance.
The American Dietetic Association’s (ADA) position statement on Nutrition and Athletic Performance, written in conjunction with the Dietitians of Canada and the American College of Sports Medicine, have made specific references to the effects of Vitamin-D. Its effects were described both as an independent supplement, and in addition to other micronutrients influenced by Vitamin-D.
The ADA’s position statement also describes that Vitamin-D is required for a number of functions, which include adequate calcium absorption, regulation of serum calcium and phosphorous levels, promotion of bone health, and regulation of homeostasis and development of the nervous system and skeletal muscles.
Risk Factors for Vitamin-D Deficiency
The position statement points out that vegetarian athletes are at a higher risk of being Vitamin-D deficient. Common dietary sources of Vitamin-D include wild-caught fatty fish (a food that would obviously be absent from a vegetarian’s diet). However, the primary source of Vitamin-D for humans is through ultraviolet-B radiation, which is obtained via direct sunlight exposure.
Various factors appear to influence how much sunlight exposure is required to influence the amount of Vitamin-D that the body is able to synthesize. Latitude, season of the year, time of day, sunblock, melanin content of the skin, age, and clothing are a few of these factors.
A 2009 study suggested that individuals who train and/or compete above the 35-degree latitude marker (which is half of the United States and all of Canada and Europe), do not receive enough sun exposure to synthesize enough Vitamin-D. This is especially evident during the fall and winter seasons. Others who may be at risk are those who engage in indoor sports or train primarily indoors, such as gymnasts, indoor track and field athletes, basketball players, and wrestlers. There was also found to be a surprisingly high amount of Vitamin-D deficiency described in Miami, Florida because of the extensive use of sunblock.
Optimal Vitamin-D Levels and Health Implications
The rates of Vitamin-D deficiency are changed almost yearly, as the laboratory levels used to determine adequate or inadequate levels of Vitamin-D in the blood serum change. Recent studies have determined that “ideal” levels of Vitamin-D are at or above 50 ng·mL. This represents an increase from 30 ng·mL, which was previously thought to be adequate.
This is problematic for several reasons. One of the most critical reasons is that the number of diseases caused at least in part by Vitamin-D deficiencies appear to be on the rise. They include cardiovascular diseases, some cancers, arthritis, and diabetes. Common symptoms of Vitamin-D deficiency include bone pain, muscle weakness, dental and bone deformities, and impaired bone growth in children (referred to as rickets). In adults, Vitamin-D deficiency most commonly presents with bone pain, muscle weakness, and osteoporosis.
Vitamin-D and Athletic Performance Evidence
Research has shown that some aspects of athletic performance may be impaired when Vitamin-D levels are inadequate. In fact, a 2009 article described a 1944 study performed by Russian scientists that showed medical students exposed to ultraviolet radiation twice a week for six weeks performed 13% better than before exposure.
Another study from 1945 involved eleven male college students exposed to ultraviolet radiation who performed 19.2% better at cardiovascular fitness and muscular endurance compared to a 1.5% increase by matched control subjects. Similar studies continuing into the 1960s found comparable results, but more recent studies could not be located.
Muscle Weakness and Myopathy
Myopathy is another notable effect of Vitamin-D deficiency, especially in athletically active individuals. Initially, muscle weakness was thought to be a secondary side effect from osteomalacia (bone pain) but is now thought to be a separate and direct effect of Vitamin-D deficiency.
A study performed in 1974 documented electromyographic changes in patients with muscle weakness and osteomalacia. These changes were also noted to improve in another study from 1976. More recent studies performed in the 1990s have outlined either non-specific or Type II muscle fiber atrophy is present in those with Hypovitaminosis-D (Vitamin-D deficiency). Changes in electromyographic data have been directly correlated to athletic performance by altering factors like neuromuscular facilitation.
Vitamin-D and Muscle Pain
Muscle pain has also been linked to Vitamin-D deficiency. A 2008 study found a possible link between low Vitamin-D and muscle pain. The study reviewed 267 cases of patients presenting with chronic pain. It noted that the patients lived at or above 37 degrees of latitude and had blood serum levels of ≤20 ng·mL.
Opioid levels were also determined to factor into the patient’s perception of pain. Of the 267 cases reviewed, 69 (26%) had inadequate levels of Vitamin-D. Of these 69, 38 (55%) used opiates to help control pain, while 31 (45%) did not. There were 198 (74%) cases where Vitamin-D levels were sufficient, but 102 (52%) patients still utilized opiate drug therapies. The remaining ninety-six cases (48%) did not use opiates. Muscle pain is a potentially serious limiting factor to athletic performance and should be considered to determine specific etiology.
Vitamin-D and Calcium Regulation
Arguably the most common function associated with Vitamin-D is assisting the intake and regulation of calcium. Calcium is responsible for growth, maintenance, and repair of bone tissue, regulation of muscle contraction, nerve conduction, and normal blood clotting.
If Vitamin-D is not present in adequate levels, these functions may be impaired, resulting in potential disqualification from athletic participation. There are associated increased risks of stress fractures, acute fractures, low bone-mineral density, and menstrual dysfunction in females as a direct result of Vitamin-D deficiency impairing calcium absorption. Supplementation of Vitamin-D is often necessary in athletic individuals if lifestyle changes (in diet or increased sunlight exposure) fail to adjust Vitamin-D levels and calcium intake remains insufficient.
Summary
Vitamin-D has not been as extensively studied in recent years as it has in the past. However, much of what has been learned regarding athletic performance still holds true today. Bone abnormalities, arthritis, myopathies, and chronic muscle pain all have links to Vitamin-D levels. Deficiencies can impact athletic performance and have long-term consequences beyond athletics.
Vitamin-D has been cited by professional organizations like the ADA and American College of Sports Medicine as an important micronutrient that can directly and indirectly affect athletic performance. Although sunlight can provide adequate amounts of Vitamin-D, over half of the United States and all of Canada and Europe do not receive enough sun exposure to synthesize sufficient amounts. Serum levels of Vitamin-D should be evaluated to determine if adequate levels are present in athletically engaged individuals.
References
American Dietetic Association, Dietitians of Canada, American College of Sports Medicine. Position Statement: Nutrition and Athletic Performance 2009.
Cannell JJ, Hollis BW, Sorenson MB, Taft TN, Anderson JJB. Athletic Performance and Vitamin D. Medicine & Science in Sport & Exercise. 2009;41(5):1102-1110.
Levis S, Gomez A, Jimenez C. Vitamin D deficiency and seasonal variation in an adult South Florida population. J Clin Endocrinol Metab. 2005;90(3):1557-1562.
Heaney RP. The vitamin D requirement in health and disease. J Steroid Biochem Mol Biol. 2005;97(1-2):13-19.
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Turner MK, Hooten WM, Schmidt JE, Kerkvliet JL, Townsend CO, Bruce BK. Prevalence and Clinical Correlates of Vitamin D Inadequacy among Patients with Chronic Pain. Pain Medicine. 2008;9(8):979-984.
