May 2018 Issue
Fueling for Fitness: Vitamin D Status in College Sports
By Marie Spano, MS, RD, CSCS, CSSD
Today's Dietitian
Vol. 20, No. 5, P. 12
Is deficiency and insufficiency a growing epidemic?
More than 30% to 50% of college athletes have either deficient or insufficient serum levels of vitamin D, which can have a detrimental impact on muscle strength and power, energy production, and bone health, and can lead to higher risk of muscle injury.1-3 Suffice it to say, vitamin D deficiency or insufficiency can greatly hinder overall athletic performance.
Vitamin D status is determined by the total amount of serum 25-hydroxyvitamin D (25[OH]D). There's no consensus regarding optimal vitamin D levels for health and athletic performance.4 The Institute of Medicine describes deficiency as blood levels ranging from 0 to 11 ng/mL, insufficiency as 12 to 20 ng/mL, and sufficiency as ≥20 ng/mL. Toxicity is >50 ng/mL.5
Who's at Risk?
In general, individuals who are at greater risk of vitamin D deficiency are those who are overweight or obese, people who get little sun exposure,6,7 those with medical conditions leading to fat malabsorption, and dark-skinned athletes. Measurement of 25(OH)D only, as opposed to measuring both 25(OH)D and the active form 1,25-dihydroxyvitamin D2 (1,25[OH]D2), confounds the interpretation of vitamin D status in dark-skinned athletes, as they rapidly convert 25(OH)D to 1,25(OH)D2.8
Powerful Impact on Performance
Vitamin D deficiency and insufficiency can impair muscle contraction and relaxation; weaken type II muscle fibers (the kind used for short, rapid-fire activities, such as sprinting and jumping); and decrease strength.5,9-13 In addition, vitamin D deficiency and insufficiency are associated with an increased risk of bone injuries, including stress fractures, muscle injuries, chronic musculoskeletal pain, impaired immune system functioning, and increased incidence of upper respiratory infections.2,14-16 Lower vitamin D levels also are associated with upper respiratory tract infections and symptomatic days.17,18
Moving From Suboptimal to Optimal Levels
Studies show that vitamin D supplementation in athletes who are either vitamin D deficient or insufficient raises blood serum levels and boosts performance. Professional male athletes with deficient (<12 ng/mL; 30 nmol/L) or insufficient levels of vitamin D (12–20 ng/mL; 30–50 nmol/L) who received 5,000 IU of vitamin D3 per day for eight weeks experienced increases in mean blood levels from 11.6 ng/mL to 41 ± 10 ng/mL and saw improvements in 10-meter sprint time and vertical jumps (both of which recruit mainly type II fibers) compared with placebo.16-18 One study showed that judo athletes deficient in vitamin D (average of 13.16 ng/mL) who were given a single bolus dose of 150,000 IU vitamin D3 experienced increases in mean 25(OH)D blood levels from 13.16 ng/mL to 16.76 ng/mL and improved strength by 13% eight days after supplementation.19 Another study found that physically active men deficient in vitamin D who were given 4,000 IU per day for six weeks to achieve blood serum levels of >30 ng/mL 25(OH)D experienced greater force recovery after damaging eccentric exercise. They recovered their ability to produce force sooner compared with those given a placebo.20
While some studies show athletic performance improves significantly with vitamin D supplementation in athletes who either were deficient or insufficient, other studies show that performance doesn't improve much in those beginning with sufficient or insufficient levels. For instance, one study showed that improving vitamin D status from sufficient levels (an average of 20 ng/mL) to an average of >40 ng/mL in well-trained soccer players didn't improve power.21 In another study, adolescent swimmers with vitamin D insufficiency (mean blood 25(OH)D of 24.2 ng/mL) who were randomized to receive 2,000 IU vitamin D3 per day for 12 weeks improved 25(OH)D to a mean of 29.6 ng/mL, yet only 48% of the vitamin group became vitamin D sufficient, raising levels to >30 ng/mL. Nonetheless, researchers found no differences in strength, balance, or swimming performance between those who became sufficient and those who didn't.22 In addition, research shows supplementation in an effort to increase vitamin D levels beyond sufficiency won't improve strength or sprint speed in pro athletes.23,24
According to Meg Mangin, RN, director at Chronic Illness Recovery in Menomonie, Wisconsin, vitamin D supplementation in athletes who are deficient or insufficient may not always be a good idea, since vitamin D is associated with inflammation.25 "If something is triggering a constant immune response, 1,25(OH)D2 will be produced in high amounts, yet inflammation doesn't go away," Mangin says. "This could aggravate the inflammatory response. If serum 25(OH)D is low, measure 1,25(OH)D2 (measured in pg/mL). If 1,25(OH)D2 is high, it's important to find the cause of the immune response." In athletics, while the prevailing thought may be to load on the vitamin D if a person's 25(OH)D is in the deficient range, in those with immune system dysfunction, supplemental vitamin D may do more harm than good.
Achieving Optimal Levels
Sun exposure represents the largest contribution to vitamin D status.26 However, UV exposure should be carefully considered, as UV radiation is a carcinogen responsible for the majority of skin cancers.27 The American Academy of Dermatology doesn't recommend getting vitamin D from sun exposure.28
In one study, just 5% of college athletes consumed the Recommended Dietary Allowance for vitamin D.29 Oily fish, such as swordfish, sockeye, salmon, and tuna, are excellent sources of vitamin D. Vitamin D-fortified orange juice, milk, and some brands of yogurt also are excellent sources. Eggs and sardines are good sources, too.30 Vitamin D3 found in fortified foods and supplements typically is made from lanolin in sheep's wool or fish oil extract.25 Vitamin D2 comes from fungus, such as mushrooms, or yeast.31 Vegans can find vitamin D in fortified soymilk, almond milk, and other fortified nondairy beverages, and fortified tofu. All mushrooms contain ergosterol, a precursor to vitamin D2. When mushrooms are exposed to UV light during growth and processing, part of their ergosterol is converted to vitamin D2. However, the amount of vitamin D2 in mushrooms exposed to UV light varies depending on the type of light and length of time exposed.32
Generally, 1,000 IU of vitamin D raises serum 25(OH)D by 10 ng/mL over a two- to three-month period.33 Vitamin D is best absorbed when taken with a meal that contains fat as opposed to a fat-free meal or on an empty stomach.34
Vitamin D isn't an ergogenic aid but a biological requirement. Recommendations to consume vitamin D should be based on vitamin D status and avoiding vitamin D deficiency and toxicity. Currently, there's no convincing evidence that giving athletes supplemental doses in an effort to boost levels above a blood serum 25(OH)D of 30 ng/mL will improve performance.24 As with any nutrition intervention, an individualized approach is warranted.
— Marie Spano, MS, RD, CSCS, CSSD, is the sports nutritionist for the Atlanta Braves, Atlanta Falcons, and Atlanta Hawks. She's the lead author of Nutrition for Sport, Exercise and Health. Visit her at www.mariespano.com.
References
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19. Wyon MA, Wolman R, Nevill AM, et al. Acute effects of Vitamin D3 supplementation on muscle strength in judoka athletes: a randomized placebo-controlled, double-blind trial. Clin J Sport Med. 2016;26(4):279-284.
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23. Fairbairn KA, Ceelen IJM, Skeaff CM, Cameron CM, Perry TL. Vitamin D3 supplementation does not improve sprint performance in professional rugby players: a randomized, placebo-controlled, double-blind intervention study. Int J Sport Nutr Exerc Metab. 2018;28(1):1-9.
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