I got my blood test results back today and learned that I'm quite deficient in vitamin D. So I did a bit of online research to see what the side effects of D defiency are. You, my triathlete readers, should all know about this one!
A bit of back story: I've been struggling with muscle strength lately. Actually I've seen weakness over the past couple years, and it's gotten rather severe in the past few months. I'd compain to my coach that my muscles were always tired, I couldn't hit the numbers I should be able to hit, and I was even having trouble walking up the stairs to my apartment. I remember biking in Texas 8 years ago and gaining a lot of speed and pretty muscular quads that were too big to pack into my jeans. I haven't been able to replicate that while training for triathlon in the last two years, and I'd chalked it up to getting older and to possible overtraining.
So back to Vitamin D, which is actually a steroid hormone: while it's most commonly known for bone density and strength (stress fractures, anyone?) it's also linked to muscle strength and specifically, fast twitch muscle fiber size. A recent study of 99 post-menarchal adolescent girls in England found a positive relationship between serum Vitamin D level and jump height, jump velocity and power. Russians and Germans experimented with UV light to boost the athletic performance of their Olympic athletes; the radiated runners improved their times by 7%. source
The optimal range for vitamin D is between 50 - 70 nanograms/ml, which is common among those who live in sunny Southern climes. 30 - 50 is considered "at risk" by the CDC. Mine is only 24... I'm sure a significant drop from when I lived in Texas. Now that I'm in SF, I'm not in the sun much. Unfortunately our diets, no matter how good, can't make up for the lack of sunshine.
And seasonality counts. Studies show a drop-off in athletic performance in the off-season. While there are a number of factors for this, a drop in vitamin D is thought to play a large role. Take a look at this chart from a fascinating article, Athletes Who Take Vitamin D Perform Better, that maps the amount of D you'll get from the sun by month:
Now, "compare the curve above with the one in the graph below, which is from a German study done in the fifties, where the researchers got seven test subjects to train their lower arms. The graph shows their progression, which was highest when the concentration of 25-hydroxy-vitamin D in the blood was also at its highest." (Great justification for supplements in the off season!)
Even more important than performance is basic health. Vitamin D deficiency is linked to inflamatory bowel disease and gluten intolerance, along with low immunity and a host of other diseases like MS and bowel and breast cancers. It's not causative to IBD, but my hunch is that I had a predisposition to IBD and gluten intolerance my entire life yet living in the sun in Texas for decades kept the symptoms at bay. 6 years with minimal sun and no vitamin D supplementation in San Francisco, and my levels got low enough to become symptomatic.
My other symptoms of D deficiency include mood swings, fatigue, and depressed immune system. I'm sure these will go away once I get my levels back to normal, and in a couple months my muscle strength will return. The fatigue and weakness has been my biggest challenge for even thinking about training again, and I'm thrilled that it's such an easy fix. I'm sure my IBD won't just vanish, but perhaps it will go into remission and stay there with less struggle and diet restrictions.
About 1/3 of Americans are in the "at risk" category or below. You might be more likely to be at risk if you're in climes like the Pacific Northwest where we don't get as much sun. But even if you're in normal ranges, you may benefit from a vitamin D supplement. I'm not sure if you'll see such obvious symptoms unless you're in the 8% like me who are truly deficient, but who knows, it may be your magic performance boost for training.