I was reading some scientific papers on nutrition
and bone health which led my attention off in an interesting direction. The topic I had originally been researching
was the role of calcium in maintaining bone health (spoiler: calcium is
important!), but what really sparked my interest was the emerging science of
vitamin D. Vitamin D is something I've
long thought of as just an adjunct to calcium intake; much like vitamin C
boosts iron absorption, so too does vitamin D boost calcium absorption. But as it turns out, there is much more to
vitamin D. For one, it's really more of
a hormone than a nutrient, and strictly speaking it's not a
"nutrient" at all—even an extremely healthy and nutritious diet
hardly contains any vitamin D at all.
Most of the vitamin D in your body is synthesized by exposure to
sunlight.
With some interesting chemistry, your skin is able
to capture some of the energy from the sun's ultraviolet light, using it to kick-start
the reaction that synthesizes vitamin D from a cholesterol-like precursor. Since this is the primary source of vitamin D
for most people, blood levels of vitamin D tend to vary by season, peaking in
the late summer and dropping sharply by mid-fall. Additionally, people who spend a lot of time
indoors (including indoor athletes like gymnasts), live in northern climates
(like Minnesota, my home state), and who have dark skin are less likely to be
able to synthesize enough vitamin D through their day-to-day sun exposure.
Our understanding of the role of vitamin D in the
body when it comes to health and overall wellness is developing rapidly, but
there is still much to be learned. Vitamin
D appears to play a role in a whole host of health issues: A 2009 review
article by Cannell et al. reports that overall death rates are 26% lower in
people with the highest blood levels of vitamin D than in those with the lowest
levels,1 a paper by
Halliday et al. reports that college athletes with lower levels of vitamin D
suffered from illness more frequently,2 Judd and
Tangpricha report that vitamin D deficiency is associated with cardiovascular
disease and diabetes,3 and Plotnikoff and
Quigley report that vitamin D deficiency is an extremely common finding among
inner-city residents who complain of persistent, nonspecific musculoskeletal
pain.4 The science is developing so rapidly that the
recommended daily intake amount for vitamin D is well under what it should be,
according to some of the authors of these papers. But what interests me is not supplementation
and RDIs—that will surely be pounced upon by the vitamin and supplement
industry. What interests me most in the context of running is the seasonal
variance of vitamin D levels and performance.
I came across a review study which cites some fascinating
studies done in Germany in the mid-20th century that connected exposure to
ultraviolet light with performance gains in an astounding range of tasks,
ranging from swimming time-trials in trained athletes to general fitness tests and
reaction time in schoolchildren.1 These studies also reportedly found that
performance in the control groups varied with a stark seasonality that tracks
very closely with blood levels of vitamin D.
Unfortunately, modern studies on the effects of
vitamin D levels or supplementation on athletic performance are practically
non-existent. Research trends in
physiology seem to come and go, though why these promising German studies were
not followed up with larger and more rigorous ones is beyond me. Cannell et al. succinctly sum up what is
still unknown when it comes to vitamin D and athletic performance, and what
kind of study could address these questions:
If an effect [of vitamin D on
performance] exists, what is its magnitude? Which athletic performance
variables (reaction time, muscle strength, balance, coordination, or endurance)
improve the most? What is the optimal 25(OH)D [form of vitamin D found in the blood] level for peak athletic
performance? Do higher levels impair it? Only direct interventional studies in
vitamin D–deficient athletes will answer the athletic performance questions. A double-blind,
placebo-controlled, multiple-dose crossover study with long washout periods
using variable but relatively high physiological doses, such as 2000, 4000, and
6000 IU of vitamin D·d-1[per
day], combined with periodic 25(OH)D levels, might answer the question of
whether peak performance levels exist for any particular serum 25(OH)D.1
While supplementation is certainly an attractive
treatment for those who are in-the-know when it comes to vitamin D deficiency,
what interests me more is the natural seasonal variability in performance that
is associated with blood levels of vitamin D.
In an admittedly brief survey of the physiology literature I could find,
I found one study which explicitly addressed seasonal variance in aerobic
fitness in the laboratory. Kuipers et
al. reported no seasonal effect on VO2 max or maximum workload. Still, this study was done in the
Netherlands, which is warmer (though more northern) than some of the more
landlocked cities where, presumably, the residents get less sun exposure
overall.
Until there's more research out, we'll be left musing
on whether vitamin D has an effect on performance, and if so, how significant
it is. Should there be more super-fast
invitational track meets and road races in the late summer to take advantage of
naturally higher levels of vitamin D? Is your team's poor performance at the
end of the cross country season the result of poor peaking or simply less sun
exposure? I'll leave you with this graphic that shows the seasonal variability
in blood vitamin D levels and the training response measured from a wrist-flexor
strengthening protocol. While wrist
strength is a long ways from distance running performance, it's nevertheless a
good springboard for future research questions.
References
1. Cannell, J. J.; Hollis, B.
W.; Sorenson, M. B.; Taft, T. N.; Anderson, J. J. B., Athletic Performance and
Vitamin D. Medicine & Science in
Sports & Exercise 2009, 41 (5), 1102-1110.
2. Halliday, T. M.; Peterson, N. J.;
Thomas, J. J.; Kleppinger, K.; Hollis, B. W.; Larson-Meyer, D. E., Vitamin D
Status Relative to Diet, Lifestyle, Injury, and Illness in College Athletes. Medicine & Science in Sports &
Exercise 2011, 43 (2), 335-343.
3. Judd, S.; Tangpricha, V., Vitamin D
deficiency and risk for cardiovascular disease. Circulation 2008, 117 (4), 503-511.
4. Plotnikoff, G. A.; Quigley, J. M.,
Prevalence of severe hypovitaminosis D in patients with persistent, nonspecific
musculoskeletal pain. Mayo Clinic
Proceedings 2003, 78 (12), 1463-1470.
Hmm.. hard to think of a reason why Vit. D deficiency would directly affect aerobic performance (cardiac output, oxygen utilization, etc..). Perhaps with a weakened bone structure (or something similar)it might affect training, but that would be an indirect component to performance. A study conducted in the 1950s on wrist-flexor strength is not a very substantial claim to base further research off of.
ReplyDeleteAlso, there is NOT strong evidence to suggest that Vit. D is related to CV disease. Much more research needs to be done before making that claim.
My wife and I live in New York. We both supplement with Vit D-3 (1000 mg) in order to maintain a minimum 30 ng/mL. Depending upon the time of year, that takes between 1 and 3 capsules per day. Without supplementing we both dropped below 30 in the winter months. This was a simple fix for us.
ReplyDeleteGreat article! I have just started reading a book about the many benefits of Vitamin D. With high blood levels of vitamin D your immunity is stronger and your heart is better protected from disease along with a whole host of other benefits, all of which will improve your performance.
ReplyDeleteIf you care to check it out the book, it is written by a well known and respected investigative journalist Ian Wishart, he brings together the most up to date science on vitamin D and how it could well save your life? Im not trying to sell you the book, but merely lead you to it to form your own opinion.
Vitamin D: Is This the Miracle Vitamin?
By Ian Wishart
http://www.amazon.com/Vitamin-This-The-Miracle-ebook/dp/B008S0LH6K
P.S Really enjoy reading posts. At 44 yrs of age I'm relatively new to longer distance running, having recently completed my first half marathon, up till then the most I ran was up to 10k. Keep up the good work.
Joanne