Bone is living tissue that exists in a state of constant flux of building up and breaking down. Until the age of 30, your bones tend to build up faster than they weaken. As you age beyond 30, this process reverses itself. Regular exercise and a healthy diet--with adequate amounts of protein, calcium and vitamins D and K--can help slow down this rate of decline, but it cannot completely stop it, according to the Harvard School of Public Health.
Function
The National Dairy Council has done a good job spreading the word about the importance of calcium for bones and teeth. Calcium alone, however, is not enough to keep your skeleton strong. To properly absorb calcium, you need to maintain adequate levels of vitamin D. To maintain bone health, you need to also consume an adequate amount of protein. But to properly make use of the protein you consume, the body needs vitamin K, according to the "Californian Journal of Health Promotion."
Warnings
When it comes to calcium and protein, more is not necessarily better. High intake of calcium may cause problems such as dizziness, constipation, fatigue and poor absorption of iron and zinc. Too much protein in the diet can also cause bone degeneration. When digesting protein, the body releases acids into the bloodstream. To neutralize those acids, it borrows calcium from the bones. If you continue to borrow that calcium without paying it back, your bones may become brittle and weak, according to the Harvard School for Public Health.
Recommendations
The recommended calcium intake for adults under 50 is 1,000 milligrams. The recommend intake of vitamin D is 1,000 IU. Many supplements, however, contain only 400 IU, which reflects an older recommendation. People who have dark skin or who spend little time outside may need more. The recommended intake of protein is 0.8 grams of protein per kilogram of adult body weight. That's about 46 grams per day for the average adult female. Target vitamin K intake is 120 micrograms, equivalent to approximately one serving of green vegetables per day.
Sources
To help maintain strong bones, your daily diet should consist of foods that supply adequate--but not extreme--amounts of protein, calcium and vitamins D and K. Sardines are rich in calcium, vitamin D and protein. Green vegetables provide not only vitamin K but also calcium. Fortified cereals and juices often contain both calcium and vitamin D. Most brands of milk--naturally calcium rich--come fortified with vitamin D. You can also get your vitamin D naturally from the sun. If you are fair skinned, you may be able to meet your needs by spending 10 minutes in the sun without sunscreen twice per week. Darker skinned people and those who live in colder climates may require more time outdoors, especially during winter.
Considerations
Standard guidelines for calcium intake may be too high, according to the Harvard School for Public Health. Countries such as India, Japan and Peru have a low incidence of osteoporosis despite an average calcium intake of approximately 300 milligrams, a number significantly less than the U.S. recommendation of 1,000 milligrams. People in these countries do, however, get more sunlight and physical exercise. They also consume less calcium-depleting protein and more vegetables rich in vitamin K. Consuming one serving of K-rich greens per day instead of per week cuts a woman's risk for hip fracture in half, according to the Nurse's Health Study reported by the Harvard School for Public Health. No such evidence exists for adding additional dairy or calcium sources--beyond a single serving of milk--to the diet, according to the same source.
