Sydney Cyclist

Cycling in Sydney Australia

From: http://well.blogs.nytimes.com/2009/07/01/is-bicycling-bad-for-your-...

Not an issue, aparently, for anyone but racers, but here's the quote (emphasis added):
In his study, the bone density of 32 male, competitive bike riders, most in their late 20s and early 30s, was compared to that of age-matched controls, men who were active but not competitive athletes. Bone scans showed that almost all of the cyclists had significantly less bone density in the spine than the control group. Some of the racers, young men in their 20s, had osteopenia in their spines, a medical condition only one step below full-blown osteoporosis. “To find guys in their twenties with osteopenia was surprising and pretty disturbing,” Smathers says.

And the possible cause:
Smathers and other researchers aren’t sure why cyclists have lower bone density. From their studies they have found that body mass is a central factor. In Smathers’ study, the lightest riders had the lowest bone density. In addition, many serious riders burn more calories in a day than they consume, an energy imbalance that is being studied to determine its impact on bone loss.

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I'm no doctor but I don't quite understand how you can get vitamins from the sun. Is it not more likely that exposure to sunlight helps process the vitamins, which are already in your body from your dietary intake?

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Vitamin D doesn't come from the sun but exposure to sunlight plays a role.

A very small amount of Vit D is derived from the diet in the form of egg yolk, oily fish, butter and milk. The major source of Vit D, however, is modification of a compound in the skin called 7-dehydrocholesterol. Both Vit D and 7-dehydrocholesterol are modified steroids. When UV light from the sun falls on the skin, 7-dehydrocholesterol is converted to cholecalciferol, an inactive form of Vit D. Further chemical groups are added to cholecalciferol in the liver and kidney to form the active form of Vit D, called 1,25-dihydroxycholecalciferol or Vit D3.

Enough of the biochemistry lesson. Riding your bike on a sunny day will give you sufficient levels of Vit D3. But remember to "slip slop slap" and not get too much sun as we are the melanoma capital of the world!

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Because the slip slop slap campaign has been so effective, they recently released guidelines saying a certain amount of unprotected sun light is still needed. Need about 15 mins daily exposure in summer for enough vit d.

The Health Report on ABC had a report on latest findings about vit D and calcium too. Advice to women is to get more calcium in your diet, milk and cheese etc.

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