Introduction
Given my research background on bone health, I’d like to talk about a highly under-appreciated micronutrient: Vitamin D! It’s especially important to talk about since we are entering winter, when Vitamin D status drops because of less sunlight and exposure.
What is Vitamin D
Vitamin D is a fat-soluble micronutrient/steroid that’s mainly synthesized through our skin via exposure to UV light (specifically UVB). As taken from my grad school textbook, “Advanced Nutrition and Human Metabolism” (Gropper, Smith, Groff, pgs. 344-345):
“The steroid 7-dehydrocholesterol is synthesized in the sabaceous glands of the skin and secreted onto the skin’s surface, and may be reabsorbed into the various layers of the skin. It appears to be uniformly distributed throughout the epidermis and dermis…. during exposure to sunlight, some of the epidermal cutaneous reservoir of 7-dehydrocholesterol is converted to previtamin D3…. Much of the previtamin D3 is thermally isomerized within 2 to 3 days into vitamin D3, also called cholecalciferol….Cholecalciferol diffuses from the skin into the blood with the transport in the blood occurring via a transport α-2 globulin vitamin D-binding protein (DBP)… Because… previtamin D3 doesn’t have much affinity for the DBP, these compounds typically are lost with the sloughing off of the skin.”
Also, I highly recommend reading the following Review on Vit. D:
“…this is produced in large quantities in the skin and incorporated into plasma membrane lipid bilayers of cells in the dermis and epidermis. When the skin is exposed to sunlight, 7-dehydrocholesterol absorbs UVb radiation in the wavelength range 290–315 nm. The absorbed energy causes chemical bonds within the 7-dehydrocholesterol molecule to break and rearrange, resulting in the formation of previtamin D. In the skin, previtamin D3 undergoes rapid, thermally-induced transformation to vitamin D3….”
I had to post the above, because one of my friends directed me to some zealous guy’s post suggesting you “only wash the critical areas with soap” (Yikes!) because you will lose the absorbable Vitamin D on your skin. Well, Mr. Sunshine Guy from Florida, Vit. D is a fat-soluble steroid (~meaning it’s stored up); who’s precursor is distributed throughout the plasma membrane lipid bilayers of the dermis and epidermis; it’s rapidly and thermally isomerized by sunlight to D3 (~depends on skin temperature, warmer=better); and, absorbed through the skin into the bloodstream and bound to DBP. What isn’t isomerized and bound to DBP is sloughed off the skin. In the liver, circulating D3 is metabolized into the most common circulating form of Vit. D, 25(OH)D3– this is what’s tested in a lab to determine Vit. D status.
Also, in the review article, it talks about how the body has the ability to photoregulate how much Vit. D3 is synthesized to prevent toxic levels from being produced. Thus, even though it’s fat soluble, under normal conditions (~regular sunlight exposure), it’s next to impossible to develop a toxicity of Vit. D3– this would likely only happen with mass injected/orally consumed doses. What is most likely to happen with Vit. D3 is a deficiency.
Food Sources
I recommend checking the information at my alma mater, Oregon State: Linus Pauling Institute
As mentioned in the link, Vit. D isn’t found naturally in too many foods, and thus several common staples are fortified with it. Natural foods: fatty fishes (mackeral, salmon, sardines), fish liver oil (Cod liver oil, yum yum!), and eggs (from chickens fed Vit. D). Common fortified foods include: cereals, milk, bread, OJ, and infant formula. It’s worth mentioning– because Vit. D is FAT-SOLUBLE, it’s best to have some fat in your MILK…. don’t get non-fat milk! With milk also being rich in Calcium (and Vit. D enhancing it’s absorption), they go hand-in-hand.
Preachin’ it
Ok, here’s where I get on my soapbox and preach it…. just because you’re an athlete/runner who’s running outside in the sunshine…. DON’T ASSUME your Vit. D status is Ok. Just like I talked about with iron, because you eat meat…. don’t assume you’re getting enough iron to meet your physiological demands as an athlete.
There’s been a strong push to “protect our skin” (against skin cancer, anti-aging….). This has consequently led to an epidemic of Vit. D deficiency, which has been linked to a greater incidence to several diseases (see Linus Pauling Institute ). A few years ago, there was an article in Running Times about Vit. D. It mentioned how Deena Kastor, who has a long history of bouts with skin cancer, found out she was Vit. D deficient due to overprotecting her skin (~wearing layers and sunscreen). She had developed a stress fracture in her foot at the Beijing Olympics, just prior to finding out she was Vit. D deficient.
Even one of my friends who’s a Dietician/marathoner went to get her Vit. D status checked (in December) and found out it was sub-optimal. As athletes, we need more of everything to perform and stay healthy. The only way to know, is to get it checked, whether by a doctor or through a website such as http://www.healthcheckusa.com (which I highly recommend…. fast and cheap).
As you can tell from the above, our greatest natural production of Vit. D3 is during the summer, when we’re more exposed to the sunlight. As winter comes, because of less sun exposure and covering up with layers (or running in the dark or on a treadmill), our Vit. D status drops.
How does this affect YOU? Well, most of you likely know that Vit. D3 is used to help calcium absorption and bone health. What you likely don’t know is it’s importance to muscle health, oxygen consumption, and the immune system.
There was a NYTimes article a few years ago, “Can Vit. D improve your athletic performance?” From the article:
“…The athletes, in other words, are fittest in August, when ultraviolet radiation from the sun is near its zenith. They often then experience an abrupt drop in maximal oxygen intake, beginning as early as September, even thought they continue to train just as hard….”
Justification for tanning beds:
“A series of strange but evocative studies undertaken decades ago in Russia and Germany, for instance, hint that the Eastern Bloc nations may have depended in part on sunlamps and Vitamin D to produce their preternaturally well-muscled and world-beating athletes. In one of the studies, four Russian sprinters were doused with artificial, ultraviolet light. Another group wasn’t. Both trained identically for the 100-meter dash. The control group lowered their sprint times by 1.7 percent. The radiated runners, in comparison, improved by an impressive 7.4 percent.”
Also, from a research article on Athletic Performance and Vit. D:
“Vitamin D also increases the size and number of Type II (fast twitch) muscle fibers…. Birge and Haddad (5) found that exogenous 25(0H)D affected ne novo protein synthesis in muscle, concluding it acts directly on muscle to increase protein synthesis….Two years of treatment with even a low dose of vitamin D–1000 IU of ergocalciferol per day–significantly increased muscle strength, doubled the mean diameter, and tripled the percentage of Type II muscle fibers…”
From the Linus Pauling Institute:
“Vitamin D deficiency causes muscle weakness and pain in children and adults…. In a cross-sectional study of 150 consecutive patients referred to a clinic in Minnesota for the evaluation of persistent, nonspecific musculoskeletal pain, 93% had serum 25-hydroxyvitamin D levels indicative of vitamin D deficiency (21)….”
As far as immune health, there’s also a correlation between the drop in Vit. D status and the incidence of colds/flu. There’s an excellent article about this here . Thus, you are more susceptible to illness when your Vit. D status drops. Personally, having been taking extra Vit. D (and iron) the past 2-3 years, I haven’t had a cold since 2008– almost 4 years.
What should your Vit. D status be?
First off, the only way to know your Vit. D status is an issue is to get it checked. As I mentioned, don’t assume it’s Ok because you’re outdoors! Secondly, there’s conflicting suggestions on the ideal value. The American College of Sports Medicine recommends greater than 40 ng/ml. From reading the research studies above, they suggest you should be at above 50 ng/ml. Obviously, if you’re lower than 40, that’s an indication you need to supplement, as recommended by a doctor. Sometimes the units are given in nmol/l– to convert ng/ml to nmol/l, multiply by 2.496 (~40 x 2.496 = 99.84 nmol/l). The Linus Pauling Institute recommends a serum 25-hydroxyvitamin D level of at least 80 nmol/l (or 32 ng/ml). As I previously mentioned, you can get it checked through: http://www.healthcheckusa.com/Vitamin-D-25-Hydroxy/46955/ . However, I’m assuming to get the high doses of Vit. D requires a doctor’s prescription.
Supplementing with Vit. D
How, how much, and how long you need to supplement likely depends on how low you are and also the season. The preferable type to take is Vit. D3. Secondly, if you’re very low, a doctor may give you an injection or prescription for very large doses of D3. As I mentioned above, because it’s fat-soluble, that means you can take a large dose at one time, and your body will store it up. Because of this, leave it up to the doctor/pharmacist on how often/large the dose should be and how long to continue supplementing. Also, because it’s fat-soluble…. it’s best to take with fat! As a daily, over-the-counter supplement, there’s conflicting recommendations on the ideal and safest amount– the Linus Pauling Institute recommends 2000 IUs/day for healthy adults. The current RDA for Vit. D is 600 IUs, which many believe to be exceptionally too low (esp. winter).
Personal Experience
In the past, I would typically feel better and train better in the summer and perform better in the fall. Then I would struggle with sickness and muscle aches in the winter, and spring was usually a mixed bag of performances/health. Also, going to grad school in Oregon, which is gloomy/overcast in the winter, my advisor forewarned me about the need to supplement with Vit. D. I figured my multivitamin and Calcium supplement was enough, but in hindsight it likely wasn’t.
In 2008, I started heat training– wearing extra layers to prepare for hot marathons. I never thought about the consequences of this on my Vit. D status. Again, I assumed my multivitamin and Calcium Citrate+Vit. D supplement (plus sun exposure on my face) was enough. However, in the wintertime I would struggle with muscle soreness. However, I did start supplementing with the liquid iron in ’08, and I did not get sick in the winter of ’08-’09 (other than food poisoning).
I believe it was the Running Times article in ’09 that woke me up and made me realize I should likely supplement with more Vit. D in the winter. I inquired with my labmates at Purdue (including Clara, who did her Ph.D. on Vit. D and calcium metabolism) on the max dose I should take– they said 2,000 IUs is a safe amount. I also looked up the Linus Pauling Institute to see what they recommended, which also advised 2,000 IUs. I basically added an extra 1,000 IUs of Vit. D3 (~Spring Valley brand from Walmart), on top of the ~1,000 IUs I get from my multivitamin plus Calcium supplement. I usually take all of these in the evening time before bed and after desert/ice cream (~a little fat = enhances absorption).
I ran a monster marathon PR in fall ’09, which I wouldn’t solely say was because of Vit. D supplementation, as I had been taking it only for a few weeks. Maybe it helped maintain my VO2 max? Who knows! However, once again, I went the whole winter without illness.
At the present (in wintertime), I’ve been taking an extra ~5,000 IUs once a week, along with my daily 2,000 IUs of Vit. D. I haven’t gotten my Vit. D status checked, but I feel GREAT– no muscular soreness or injuries, and haven’t been sick in almost 4 years! I also believe I’m getting more sun exposure in Oklahoma vs. Indiana– that might be keeping my Vit. D status more elevated.
Other Thoughts
- If you currently or normally have issues with musculoskeletal soreness/injuries and illness during the winter, it could be due to low Vit. D.
- I’d suggest getting in your main daily runs at mid-day or in the afternoon (see below), or at least a few runs each week in the most possible sun. Your face actually absorbs the most sunlight, so even if your face is exposed you can synthesize some Vit. D.
- For my friends who have to run in the early morning/evening/dark (or on a treadmill or indoor track), be mindful that you likely need to supplement with even more Vit. D.
- Living further North or in a highly overcast area may esp. put you at risk of a Vit. D deficiency. However, as mentioned on page 121 of the Review on Vit. D, research studies have even found Vit. D insufficiency in sunny climates (~Hawaii, South Florida, Southern Arizona). Don’t assume because you’re in a sunnier climate that you’re “safe”.
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As taken from the Linus Pauling Institute site: :…1 minimal erythemal dose of simulated sunlight (the amount required to cause a slight pinkness of the skin) was equivalent to ingesting approximately 20,000 IU of vitamin D2 (94)…. The application of sunscreen with an SPF factor of 8 reduces production of vitamin D by 95%. In latitudes around 40 degrees north or 40 degrees south (Boston is 42 degrees north), there is insufficient UVB radiation available for vitamin D synthesis from November to early March…. According to Dr. Michael Holick, as little as 5-10 minutes of sun exposure on arms and legs or face and arms three times weekly between 11:00 am and 2:00 pm during the spring, summer, and fall at 42 degrees latitude should provide a light-skinned individual with adequate vitamin D and allow for storage of any excess for use during the winter with minimal risk of skin damage (36).”
- Aging (>50 years) is associated with a lowered ability to synthesize Vit. D. Compounded with the push to wear sunscreen or extra layers, this population is esp. vulnerable to a Vit. D deficiency.
- This isn’t something I personally do (~supplementing is cheaper), but visiting a tanning bed may not be a bad option in the winter. It also looks like you can purchase a ”sunlamp” to use at home, but you should likely discuss this with a doctor on the safety. If any of my friends personally do this, feel free to share your experience.
- Athletes with darker skin/African descent need longer UV exposure to produce an equivalent amount of Vit. D3. The melanin acts as an ever-present sunscreen. The study above on athletic performance and Vit. D said that those with greater melanin in their skin may need up to 10x longer exposure to produce an equivalent amount of Vit. D as a fair-skinned person. This is probably why it’s more advantageous for Africans in America to live further South.
References
Athletic Performance and Vit. D
“Can Vit. D improve your athletic performance?”
Healthcheckusa.com 25-hydroxyvitaminD serum test
Wow – this is amazing information! I really think you should write a book, Camille. Something that really focuses on the Science of Running. I actually think I am going to get my Vit. D checked as a result of reading this.
Yeaaa, glad you like it! Definitely, go get checked. You know, I just might write a book some day! I’d like to achieve greatness first.
Your site is so helpful! My husband and I really appreciated your article on NSAIDs. That was vital information for runners and athletes. Wow, we are so fortunate to have found your blog, thanks for sharing your studies and knowledge!
Awesome! Glad you like my website! I’ve had so many experiences, as both a researcher and elite athletes, so I felt the need to share everything. Feel free to subscribe to my blog. I’m going to keep posting “juicy articles”– hitting on all the million dollar questions people have.