Endurance Athletes and Vitamin D: An Overview

We recently wrapped up a summer campaign, entitled #30SaltyDays, that highlighted the importance of the four major electrolytes contained in our product SaltStick Caps. The campaign lasted four weeks, which meant each electrolyte (sodium, potassium, magnesium and calcium) received its own week’s worth of content. However, SaltStick Caps also contain Vitamin D, which among other things, helps with absorption of calcium and magnesium. We think Vitamin D deserves its time in the spotlight, so read on!

How does the body use Vitamin D?

“We are only just beginning to understand the complexity and importance of Vitamin D in relation to health,” writes Competitor contributor Reyana Ewing, MPH, RD, CLE. “Of importance to athletes is the function of Vitamin D as it relates to overall health, bone density, innate immunity, muscle wasting, and exercise-related inflammation and immunity. To train and race optimally, an athlete should not have any nutrient deficiencies.” She’s right. Vitamin D -- which is produced by our bodies when we are in the presence of UVB rays from the sun or absorbed from our diet -- is essential to more than 100 biochemical processes. Athletic performance aside, low Vitamin D levels have been linked to many common cancers, multiple sclerosis, rheumatoid arthritis, hypertension, cardiovascular heart disease, and type I diabetes. Of course, we know you came here to see how Vitamin D impacts running. Rest assured, many studies have indicated that it does. Allow us to elaborate: Maintaining Bone Health: A 2004 study of Finnish military men found subjects were at risk for sub-maximal peak bone mass during the winter months, in which little sunlight exists to help produce Vitamin D. Another study (2008, Journal of Bone and Mineral Research), which examined 3,700 female navy recruits, found that active women who received 800 IU/day of Vitamin D for eight weeks suffered 20 percent fewer stress fractures than a placebo group. This same study notes that up to 31 percent of Track & Field athletes have suffered or will suffer a stress fracture. Key takeaway for runners: Vitamin D can help reduce the odds of getting a stress fracture, which could sideline your training for months as you recover. Absorbing Calcium: One reason Vitamin D is so effective in helping to prevent stress fractures is its role in calcium absorption. However, calcium does much more in the body than build strong bones. As we pointed out in our recent #30SaltyDays blog post, calcium is also vital for muscle contraction, and it can assist in weight loss, fat burning and reducing stress. Nevertheless, without Vitamin D, each of these processes is hampered (2010, Current Sports Medicine Reports) because the body cannot absorb calcium from the intestine without adequate Vitamin D levels. It responds by leaching calcium from the bones -- not good for runners who endure the daily pounding of their exercise lifestyles. Key takeaway for runners: In order to obtain the full benefits of calcium, you need adequate Vitamin D levels. Muscle Strength: Several studies of older populations have found that Vitamin D status is positively associated with muscle strength and physical performance and inversely associated with risk of falling (2013, Calcified Tissue International), indicating Vitamin D is essential in maintaining strength and operability during the aging process. What about the younger population? A separate study, published in the Journal of Endocrinology and Metabolism, found that Vitamin D levels were positively associated with muscle power and force in adolescent girls. Key takeaway for runners: Low Vitamin D levels could impair your strength, which could compromise your ability to maintain good form. (Keep reading: For the non-runners out there, here are 15 more benefits of Vitamin D.)

Should endurance athletes care about Vitamin D?

Anyone who followed the marathon event in the 2008 Olympics will remember that Deena Kastor -- a favored U.S. athlete -- broke her foot midway through the race. Blood tests later showed that Kastor’s Vitamin D levels were low, which was preventing her body from absorbing enough calcium to maintain strong bones. “Something I've prided myself on is taking care of my skin because of repeated bouts of skin cancer -- always wearing hats, long sleeve shirts, lots of sunscreen -- but I guess it's something I need to balance,” Kastor told Runner’s World. Kastor’s experience illustrates the importance of including Vitamin D in a runner’s nutrition plan -- especially with all the intense pounding that comes with the running territory. Calcium is lost through sweat and other exercise-related processes, and the body responds by releasing hormones that tell the intestines to absorb more calcium from food. However, like we said above, Vitamin D is essential for calcium absorption, and when the body cannot absorb enough calcium from the diet, it will leach calcium from bones. This weakens bones, and can result in stress fractures, or in Kastor’s case, broken bones. (Check out our August #30SaltyDays blog post for more information on the relationship between Calcium and Vitamin D here.) Research -- dating as far back as the 1950s -- also backs up Vitamin D’s importance to athletic performance. Several German and Russian studies have concluded that ultraviolet light (particularly the UVB rays that cause the body to produce Vitamin D) improves athletic performance in time trials, cardiovascular fitness, and strength (2009, Medicine and Science in Sports and Exercise). Also, while most long-distance athletes plan their seasons around an “A race” in the fall, researchers also noted that endurance athletes tend to be “most fit” during the same months that Vitamin D production peaks -- late summer and early fall. Bottom line: As a runner, you cannot be at your peak fitness level with low Vitamin D levels.

What does a Vitamin D deficiency look like?

A 2010 Current Sports Medicine Reports article concluded that “although research has found that athletes generally do not meet the U.S. dietary reference intake for vitamin D, inadequate endogenous synthesis is the most probable reason for insufficient/deficient status.” That’s a fancy way of saying diet aside, the body doesn’t produce enough Vitamin D from sunlight. (In fact, it’s assumed that 77 percent of people, athletes included, do not consume enough Vitamin D.) Due to reduced time in sunlight and frequent usage of sunscreen*, it’s easy for runners to be out in the sunlight all day and still become Vitamin-D-deficient. Additionally, if you have dark skin, live in a Northern climate or rarely venture outdoors, it may even be necessary to take a Vitamin D supplement. *(Note: This is not to say sunscreen isn’t important -- just to highlight the greater importance of a Vitamin-D-rich diet.) What are the symptoms of a deficiency? Feeling weak: In a 2013 meta-analysis of Vitamin-D-related research out of Central Washington University, authors noted that a common symptom of Vitamin D deficiency is muscle weakness. Researchers also noted that low Vitamin D levels could negatively impact physical performance. Feeling unmotivated: In a 2006 cross-section of older adults, Vitamin D deficiency was associated with low mood and with impairment on two of four measures of cognitive performance. Additionally, those with the lowest levels of vitamin D were 11 times more prone to be depressed than those who received healthy doses. Realize that both of these symptoms are caused by a myriad of factors, including lack of sleep, overtraining, bad diet, and low levels of other nutrients such as calcium or magnesium. If you suspect low Vitamin D is the cause, it’s important to work with your doctor to monitor your levels to ensure low Vitamin D is the cause.

Who is at risk for a Vitamin D deficiency?

● Most of the United States in the winter: Researchers estimate that low levels of Vitamin D are widespread in populations living beyond the 35th parallel, because the sun’s UVB rays cannot reach past this latitude in the winter. In the U.S., the 35th parallel creates the border between Tennessee and Alabama. It cuts through California, Arizona, New Mexico, South Carolina, Arkansas, Oklahoma and Texas, leaving a majority of states above the 35th parallel in winter.

● People who wear a lot of sunscreen: In addition to Kastor’s anecdotal evidence of sunscreen’s detrimental effects on Vitamin D levels, a 2008 Nutrition Review article noted that sunscreen rated SPF 15 and higher can reduce Vitamin D absorption by as much as 99 percent.

● People who work out in the evenings or early mornings: You don’t have to live above the 35th parallel to miss out on Vitamin D production. In 2010, researchers found that 91 percent of Middle Eastern male athletes were vitamin D deficient between the summer months of April and October. While the athletes lived in Qatar (25.4°N, well below the 35th parallel), they averaged less than 30 min of sun exposure per day due to the extreme heat. If you like to beat the summer sun by training in the early morning or late evening, you could be at risk for low Vitamin D.

● People with darker skin: Melanin (the pigment in the skin that makes it darker) inhibits Vitamin D production by blocking UVB rays from the sun. While lighter skinned individuals can produce 10,000 to 20,000 IU of Vitamin D in just 30 minutes of sun exposure, darker skinned individuals may take two to five times as long to produce similar amounts of Vitamin D.

Put shortly, nearly everyone is at risk for Vitamin D levels, which is likely why low levels of the nutrient are so widespread (Remember from above that 77 percent of U.S. adults to not have adequate levels). That is why it is so important to be aware of what a deficiency looks like. Runners should also check their diets to make sure they are consuming enough of the nutrient through natural sources or through supplementation.

How should endurance athletes incorporate Vitamin D into their daily diets?

The best and most efficient way to obtain Vitamin D is to spend time outdoors in direct sunlight without sunscreen. Nevertheless, this comes with its own complications -- most dermatologists agree that any direct sun exposure can be detrimental to skin cells’ health. We suggest you consult with your doctor to determine the correct balance, but if you want to avoid sun exposure entirely, it may be wise to consider a Vitamin D supplement. What about Vitamin D2 vs D3? If you choose to go the supplement route, you’ll quickly notice that some supplements contain Vitamin D2 and others contain Vitamin D3. Chemically, these two are different forms of Vitamin D, and thus, they have different properties. D2 is created from yeast-based products, whereas D3 is sourced from animal products, which means only D2 is technically vegan. However, the human body produces D3 when exposed to sunlight (so it can be argued that D3 is more “natural”), and D3 is also much more easily absorbed through the intestines. Nearly all nutrition experts agree that D3 supplementation is optimal. D3 is also much more likely to be used in clinical trials during research about Vitamin D and its effects. For these reasons — especially because D3 is more easily absorbed — SaltStick Capsules contain the D3 form of Vitamin D. Supplementation and Vitamin D toxicity: Another concern with supplementing Vitamin D is the danger of consuming too much. The National Institutes of Health officially recommends men and women get between 400 and 800 IU of Vitamin D per day, depending on age. While a 30 minutes in the sun could produce 10,000 IU of Vitamin D in fair-skinned individuals, the body will not produce more Vitamin D after more time in the sun. (Effectively, the body prevents itself from producing too much Vitamin D). However, there is no such “shut-off mechanism” when consuming Vitamin D from supplements. The NIH recommends that levels of 4,000 IU per day and below are probably harmless, but it cautions against consuming more. With some supplements containing as much as 1,000 IU of Vitamin D per serving, the dangers of consuming too much are real, and you should be aware of them. Natural dietary sources of Vitamin D: As far as diet goes, cold water fish provide (among other beneficial things such as omega-3 fats and protein) significant amounts of Vitamin D. Additionally, some fish, like sardines and salmon, that contain bones are also great sources of calcium. This makes cold-water fish super-dense sources of nutrients that are important to all runners. Other great sources of Vitamin D include eggs and fortified milk. Try including the following items in your diet to help ensure you’re getting adequate Vitamin D levels. Remember, if you have dark skin, live in a Northern climate or rarely venture outdoors, consider taking a Vitamin D supplement.

● Halibut, Greenland, 3 oz — 932 IU

● Salmon, fresh, wild caught, 3 oz — 619 IU

● Mackerel, Atlantic, 3 oz — 547 IU

● Shitake mushrooms, dried, 4 oz ­— 196 IU

● Sardines, 3 oz — 164 IU

● Tuna fish, 3 oz — 154 IU

● Herring, Atlantic, 3 oz — 142 IU

● SaltStick Capsule — 100 IU

● Fortified milk, 1 cup — 98 IU

● Egg, 1 — 25 IU

Important Note: The above should not be construed as medical advice. Contact your physician before starting any exercise program or if you are taking any medication. Individuals with high blood pressure should also consult their physician prior to taking an electrolyte supplement. Overdose of electrolytes is possible, with symptoms such as vomiting and feeling ill, and care should be taken not to overdose on any electrolyte supplement.