Vitamin D For Athletes by Lori Stevens, RD, LDN, CNSC

Posted: July 8, 2010 in Cycling, Information, Nutrition, Running, Swimming, Training Information

There has been a lot of talk about vitamin D lately.  Originally associated with the childhood disease rickets, vitamin D has reemerged as an important factor in health and disease prevention. In fact, the studies have been so convincing, health organizations and our government are considering officially increasing the recommended daily requirement for vitamin D in the diet.  It is estimated that 75% of US teens and up to 60% of adults are deficient in vitamin D.

There is a lot of information to sort through, along with some interesting recommendations as to how much vitamin D is enough, and how much vitamin D is optimal for good health.  I will do my best to sum it up as well as highlight why vitamin D may be especially important to you as an athlete!

Unlike other vitamins and minerals, vitamin D is a type of steroid hormone that has a myriad of affects on many cells and systems in the body.  We obtain vitamin D in two ways—from the diet and from the sun striking unprotected skin.  As a dietitian I usually prefer people to obtain their nutrients from foods.  Unfortunately, getting vitamin D from the diet is difficult.  Milk and oily fish are good sources but few other foods provide significant amounts.  Traditionally humans got all the vitamin D they needed from the sun.  When sun strikes skin, the body is able to make vitamin D.  However, levels typically plummet in winter when people spend more time covered up and indoors.  Our skin is more exposed in summer, but sunscreen blocks the skin from making Vitamin D.  And the farther one is from the equator, the less vitamin D is synthesized during sun exposure—even in summer.  Getting your vitamin D from the sun also poses a significant risk of skin cancer.  Skin cancer rates are rising and most dermatologists shudder at the thought of people forgoing sunscreen and protective clothing to obtain vitamin D.   In the case of vitamin D, supplements seem to be the best option.  Vitamin D supplements are inexpensive and easily available in grocery stores and pharmacies.

So why is this vitamin so important?  Vitamin D is usually associated with bone health due to the fact that it regulates calcium.  However, new research has found that vitamin D may be helpful in preventing certain cancers such as colorectal cancer.  Vitamin D also plays a role in the proper functioning of the immune system and may prevent the development of autoimmune diseases like Type 1 Diabetes and rheumatoid arthritis.  It is well known that people with Multiple Sclerosis are often vitamin D deficient.  In fact, the risk of MS is much higher the farther one lives from the equator.  Vitamin D is also believed to play a role in heart health, cholesterol levels, hypertension and Type 2 diabetes.  New research is turning up almost daily with much of it being conducted in northern states, Canada and other nations at high latitudes where a great percentage of the population is deficient.

In addition to the benefits mentioned above, it turns out that there is a relationship between vitamin D and athletic performance that may be of particular interest to you as a triathlete.  Studies dating back to the 1950’s, particularly in Germany and Russia show that vitamin D improves athletic performance.  It is well known that Olympic athletes from these countries routinely used ultraviolet lights to improve muscular strength.  And it is indisputable that athletic performance is seasonal—it peaks during the month of August when vitamin D levels are highest and drops off sharply in September.  It turns out that vitamin D works by increasing the size and number of Type II or “fast twitch” muscle fibers.  Studies with athletes of all ages demonstrate increased muscular performance is correlated with higher blood levels of vitamin D.  Few of us would turn down the opportunity to increase our muscle strength and fast twitch muscle fibers in such an easy, pain-free way!

The first thing you should do is find out your vitamin D level.  Luckily, a simple blood test called a “25OH Vitamin D” test can be ordered by your physician.  A result of 32 ng/dl or above is considered adequate.  However, many physicians and sports dietitians recommend a blood level of 50 – 60ng/dl for optimal athletic performance.  If your vitamin D levels are very low, your physician may order a prescription of high dose vitamin D to be taken once per week and then a recheck of levels in 6-8 weeks.

Most people do not need a prescription and can easily correct a low level and maintain adequate levels with vitamin D supplements found over the counter.  Taking 1000 IU of vitamin D daily along with a multivitamin that contains 200-400 IU during the spring and summer months should be enough.  More may be needed in winter.   Over this past winter I took a total of 2000 IU per day and my level was only 41ng/dl in March—a low normal reading.  Next year I plan on upping that to a total of 3000 IU daily with testing every 6 months.  But everyone is different and you may require more or less to maintain adequate blood levels.  This is why working with your physician and getting levels checked regularly is so important.  One final note, be careful not to take mega doses without your doctor’s recommendation.  Vitamin D can be toxic in very high amounts, so more is not necessarily better.

Lori Stevens RD, LDN, CNSC
WakeMed Cary Hospital

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