It used to be that cycling caused testicular cancer.
Then it was erectile dysfunction.
Then it was prostate cancer.
Now it's bone loss.
It's all hysterical nincompoopery. Some of it hyped in order to sell weirdly shaped saddles.
This study reported in the New York Times claims that cycling causes near-osteoporosis. But you have dig down pretty deep into the article to realize that the study had to do with serious competitive cyclists -- guys who ride six hours a day and who routinely starve themselves in order to fly up mountains at high altitude.
Personally, I've broken two bones in separate crashes. But that was because, in the first crash, I was being stupid and, in the second crash, I was hit by a car. Nothing there to indicate that brittle bones were to blame. The only real culpret, in the latter instance, was my body ricocheting off a car and then slamming onto the road.
In a normal week, I ride around 100 miles (with climbing) and I'm pretty serious about it. But pro riders ride around 100+ miles a day, year round. That's a lot. So if this study is at all accurate, your bones won't be disintegrating if you hop on your bike for a three mile jaunt around the neighborhood. My bones won't be disintegrating either and I ride a lot more than that.
Here's an interesting point of discussion, though. It's about sunscreen. Sunlight helps the body produce Vitamin D which, in turn, fuels the body's production of calcium which, in turn, helps the bones. But a lot of people slather themselves with sunscreen and that inhibits the natural Vitamin D boost provided by sunlight (it also injects your body -- pours open -- with whatever weird chemicals are in sunscreen, but that's another discussion). So, if this bone loss study is accurate, sunscreen might be a factor when, perhaps, combined with other things like intense lactic acid production, and the fact that milk -- loaded with fat -- usually isn't on the training table of a rider who's watching his weight.
Either way, go ride your bike and don't worry about it. Trust me -- it won't screw with your plumbing. And it won't snap your bones like twigs (unless you're hit by a car). The fitness -- both mental and physical -- provided by cycling far outweighs any dodgy claims about your balls or bones.