An estimated 1 billion people worldwide, across all ethnicities and age groups, have a vitamin D deficiency according to a review published in the Journal of Pharmacology & Pharmoacotherapeutics . Vitamin D is a steroid hormone that regulates > 1,000 processes in the body, and it has been well known as the “sunshine” vitamin playing an important role in preventing illnesses like, osteoporosis and rickets . Winter days are often dark and sun exposure is limited leading to an increased risk for vitamin D deficiency and infections. Vitamin D is a hormone but is most widely known as a fat-soluble vitamin. Vitamin D promotes calcium absorption in the gut. Vitamin D supports muscle function, cell growth and immunity. Vitamin D is obtained from supplements, sun exposure and consuming vitamin D-containing foods like, wild salmon, eggs, mushrooms, fortified cereal and dairy products.
How Much Vitamin D Is Needed?
One confusing element of understanding vitamin D guidelines to correct deficiency can be challenging. Currently, there is no consensus definition of vitamin D deficiency according to the U.S. Preventive Services Task Force recently reviewing vitamin D screening. The Institute of Medicine (IOM) guidelines for vitamin D use a blood level of 20 ng/ml o 25-hydroxyvitamin D as a benchmark for deficiency because it is the minimum level that meets the needs for good bone health for at least 97.5% of the population (1). However, the Endocrine Society recommended that people aim for a level of 30 ng/mL or higher . A more comprehensive table of Vitamin D concentrations and health are found here via the National Institute of Health.
Current Recommended Dietary Allowances (RDA) for Vitamin D:
- Birth to 12 months: 400 IU
- Children 1-13 years: 600 IU
- Teens 14-18 years: 600 IU
- Adults 19-70 years: 600 IU
- Adults 71 years and older: 800 IU
- Pregnant and breastfeeding women: 600 IU
Vitamin D Deficiency Signs and Symptoms that Can Lead to Severe Health Complications:
- Risk of stress fractures
- Muscle aches and weakness
- Muscle twitching
In the Body, Vitamin D is Linked with:
- Immune function
- Blood pressure regulation
- Muscle strength and mass
- Absorption of calcium
- Healthy weight management
- Overall bone and teeth health
Vitamin D and Athletes
Numerous studies reviewed in the Journal of the International Society of Sports Nutrition has assessed the possibility for vitamin D’s impact on performance and recovery. In fact a study published in the Journal of Strength and Conditioning Research examining soccer players who supplemented with 5,000 IU of vitamin D per day for a total of eight weeks had interesting results. Those that supplemented jumped higher and were linked to faster sprints.
A vitamin D deficiency in athletes increases the risk for stress fractures, anemia and a weaker immune system which and blunt athletic performance. A 2008 study examining Vitamin D status in a group of distance runners found that forty percent of the runners, who trained indoors in sunny Baton Rouge, Louisiana had insufficient vitamin D. deficiency is common among athletes and enough levels are needed to maintain bone health and aid in injury repair. A review carried out in 2015 identified about 56% of athletes had inadequate levels of vitamin D. Another study evaluating vitamin D levels in athletes participating at the NFL combine found that players with a history of lower extremity muscle strain an core muscle injury had a greater prevalence of inadequate vitamin . Furthermore, another study assessing association of vitamin levels with race and found a higher rate of vitamin D deficiency among black football players than white football players.
As stated above musculoskeletal pain and weakness are often unrecognized symptoms of vitamin D deficiency. A study conducted in Minnesota identified 93% of individuals with persistent non-specific musculoskeletal pain had 25(OH)D concentration <20 ng mL and 28% had a concentration <8 ng mL. Animal studies have also reported that vitamin D deficiency leads to the atrophy of fast-twitch muscle fibers, which are critical in power movements like sprints. Fast-twitch fibers also fatigue faster which can explain the physiological why vitamin D can influence based on its function.
As you have learned, vitamin D deficiency is overlooked and should be a focus of concern for any professionals working with athletes. The strong association in muscle fatigue and low vitamin D levels in elite and collegiate athletes may lead to long-term injuries with life and career altering effects. An article published in the American College of Sports Medicine provides charts and illustrations representing the vitamin D status in athletes living in various geographic locations.
To Supplement or Not Supplement?
Upon reading this article you can see how challenging it is to achieve daily vitamin D needs from foods and limited sun exposure. Provided the critical role vitamin D plays in our mood, digestion, cognition, recovery, athletic performance and overall health it would be wise to supplement with 1,000 to 2,000 IU of vitamin D3 per day during the winter solstice months and likely even more if you fall into any of the high-risk categories for vitamin D deficiency. Justifying a greater need for vitamin D for athletes who train often and participate in multiple sports. Disclaimer, I am not a physician and I would encourage you to discuss vitamin D testing with your doctor to ensure you’re not reaching toxicity, which can occur with high-dose vitamin D intakes of 60,000 IU per day. Blood levels should be monitored by anyone who chooses to take higher dose of vitamin D. As always, talk with your doctor and sports medicine staff before taking any vitamin and mineral supplements. Interested in learning more about your vitamin D status? Check out the website of the Vitamin D Society for more information. Other great resources to learn more about vitamin D include ,the Linus Pauling Institute and the National Institute of Health fact sheet for health professionals.
Check out my previous blog highlighting the six risk factors for vitamin D deficiency.
In good health,
Wendi Irlbeck, MS, RD, Sports Nutritionist