More about cycling and bone strength

[Zen]

Dr. Gabe Mirkin's Fitness and Health E-Zine
November 1, 2009

No Evidence Cycling Weakens Bones

No data exists in the scientific literature showing that
any type of exercise weakens bones. Bone growth depends on the
forces exerted on them by gravity and contracting muscles. So any
activity or exercise that causes you to contract your muscles will
strengthen bones (Medicine & Science in Sports & Exercise,
November 2009).
Previous studies showed that world class cyclists had
reduced bone densities in their spines. However, bone density
tests do not measure bones strength. They measure how much bones
block X-rays that try to pass through them. The only way to measure
bone strength is to see how much force it takes to break a bone.
The most likely explanations for broken bones in cyclists
are high-impact crashes and/or lack of vitamin D. I recommend
that all cyclists get a blood test called Vitamin D3 in December or
January. If it is below 75 nmol/L, they are deficient in vitamin D
and at increased risk for breaking bones. To prevent fractures,
they should do winter training in the southern sunbelt or take at
least 800 IU of Vitamin D3 per day.
A recent review of 12 blinded, controlled scientific
studies showed that oral vitamin D reduced non-vertebral and hip
fractures in patients over 65 years of age (Evidence-Based Medicine,
October 2009). Blood levels of vitamin D below 75 nmol/L cause
parathyroid hormone levels to rise too high, which causes
osteoporosis. A main function of vitamin D is to increase calcium
absorption from the intestines into the bloodstream. When blood
levels of vitamin D fall below 75 nmol/L, levels of ionizable
calcium drop. This causes the parathyroid gland to produce large
amounts of its hormone. Higher than normal blood parathyroid
hormone levels take calcium out of bones to cause osteoporosis.

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Gabe Mirkin, M.D.
10901 Connecticut Avenue, Kensington MD 20895, USA

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[Biciclista]

thanks . I think the suggested dose of 800 units is a little low.

[OakLeaf]

So what he's saying isn't really related to cycling at all - he's saying that DEXA scans etc. are great for selling pharmaceuticals but irrelevant to risk of fracture.

Figures.

[spokewench]

Something about that articles bothers me? - Breaking bones is due to a Vitamin D Deficiency and Cyclists should get the test. Am I wrong or is vitamin D gained through exposure to sun, as well as other things? Don't cyclists get a lot of vitamin D exposure? I know I always have; even if I try to wear sunscreen (not always successful).

spoke

[SLash]

Something about that articles bothers me? - Breaking bones is due to a Vitamin D Deficiency and Cyclists should get the test. Am I wrong or is vitamin D gained through exposure to sun, as well as other things? Don't cyclists get a lot of vitamin D exposure? I know I always have; even if I try to wear sunscreen (not always successful).

spoke

Not necessarily, I am in the sun a lot, between swimming, riding and yard work, and I tested low for Vitamin D (32 ng/ml) a couple of months ago. I was shocked because of how much time I spend outside, but my doctor said that studies have shown the sun isn't an adequate source of Vitamin D for people over ages 35-40 (I'm 55). Prior to testing me he said if my level was normal he wanted me to take 1,000 IU a day, and if it was low 50,000IU in one pill, one time a week for 12 weeks, then retest, if it is normal he will put me on 1500 IU daily for life, if it is still low 50,000 IU for 12 more weeks. I trust my doctor, he's excellent, and he says low Vitamin D is one of the most mis-diagnosed and misunderstood health problems (because of the other health issues it causes)that people have that could be easily treated and isn't.

[xanesdoc]

+1 SLash. I live in Atlanta and spend at least 5 days a week outside playing tennis, golf or riding my bike. When my GYN wanted to check my Vitamin D level two years ago, I laughed and said mine will be sky high. Well I was shocked when it came back at 6! After taking 50,000 units of Vit. D weekly for 3 months, my level increased to 54. I currently take 50,000 every 2 weeks and my levels stay between 50-60. I now wonder if I need to get it into the 75 range. I will check with my MD.