A study comparing the effects of vitamin D and calcium fortified milk with or without exercise, and exercise alone, showed that exercise provided a bone mineral density increase, but the fortified milk alone did not increase bone mineral density.
The study was done on men aged 50-79
Osteoporosis Canada recommends that adults over age 50 should have 1200mg/ day calcium, and 800 to 2000 IU/ day of vitamin D.
Meeting the daily vitamin and mineral requirement is essential, but exercise, specifically weight bearing exercise like jogging or weight training, is also critical.
It's important to note that the study protocol used a progressive resistance training model, meaning that the subjects gradually increased the loads they lifted as they became stronger. Staying with light weights doesn't cut it. Impact exercise like jogging and jumping are also potent bone builders, but like all exercise, more intensive activities should be added only as overall strength and physical ability increases.