They say to prevent Osteoporosis we should

Exercise: The best to increase bone density and reduce fractures is body weight exercises (like calisthenics) and resistance training. Make a habit of doing these exercises two or three times a week. Thirty minutes of walking a day will lower your risk of fracture by 30 percent.

I guess they should have been more specific as to WHERE to walk. If you walk on the pavement of manhattan, instead of preventing yourself from this horrible horrible osteoporosis disease, you'd prolly find yourself dead from breathing in too much 2nd hand smoke/weed and pollution from vehicles.

What then, is the point?