Your bones are made of collagen fibres filled in with calcium and other minerals to create a hard structure.
take a daily calcium supplement providing 400- 600mg of calcium, preferably one that also contains vitamin D. Take supplements with food to help aid calcium uptake into your body.
A suntan does NOT indicate you have enough vitamin D. The best way to get enough vitamin D is to take supplements, such as cod liver oil, or a multivitamin. Cod liver oil supplements are the most concentrated form, providing 10mcg (400IU) in 1-2 teaspoons per day. Fish oil capsules contain only a little oil, and often do not provide more than the basic recommended amount of 5mcg (200IU) a day. If you take a fish liver oil supplement you do not need to take a multivitamin as well that day.