Bone is a living, dynamic, metabolically active tissue. It is also a specialized connective tissue, composed of a collagen (protein) framework, permeated with mineral salts composed of mostly calcium and phosphate, together with trace amounts of other minerals and ions.
It is estimated that worldwide an osteoporotic fracture occurs every 3 seconds. At 50 years of age, one in three women and one in five men will suffer a fracture in their remaining lifetime. For women this risk is higher than the risk of breast, ovarian and uterine cancer combined. For men, the risk is higher than the risk for prostate cancer. Approximately 50% of people with one osteoporotic fracture will have another, with the risk of new fractures rising exponentially with each fracture.
A healthy, balanced diet containing both macronutrients (protein, fat and carbohydrate) and micronutrients (vitamins and minerals), plus sufficient calories, is therefore vital for both the normal development and on-going maintenance of the skeleton.
The importance of Calcium and Vitamin D in bone health
Calcium is a major structural component of bone tissue. It is deposited in bone as hydroxy-appatite which confers strength to the skeleton. Approximately 99% of calcium is stored in the bones and teeth. Vitamin D is also essential for the development and maintenance of bone, both for its role in assisting calcium absorption from food in the intestine, and for ensuring optimal formation and mineralization of bone tissue.
Milk and other dairy foods are among the richest and most readily available sources of calcium in the
diet. Two or three servings of dairy foods a day (e.g. a serving would be a glass of milk, a slice of cheese, or a medium container of yoghurt) would ensure that virtually all children and adults would achieve this level of calcium intake. Dairy foods have the additional advantage of being good sources of protein and other micronutrients (besides calcium) that are important for bone and general health. Other food sources of calcium include certain green vegetables (e.g. broccoli, curly kale, bok choy): whole canned fish with bones such as sardines or pilchards; nuts (almonds and Brazil nuts in particular); and tofu set with calcium. Calcium-fortified foods and drinks, including breads, cereals, orange juice and soy beverages are also available in some countries.
Vitamin K is needed for the production and functioning of osteocalcin. Osteocalcin is the second most abundant protein in bone after collagen, and is required for bone mineralization. Good food sources of vitamin K include leafy green vegetables such as lettuce, spinach, cabbage and kale, liver, and some fermented foods such as fermented cheeses and natto (fermented soybeans).
The mineral magnesium is important for calcium homeostasis and in the formation of hydroxyapatite (bone mineral). Severe experimental magnesium deficiency results in impaired bone structure and function, but this level of depletion is rarely observed in generally well nourished human populations.
Magnesium is fairly widespread in the food chain; particularly good sources include green vegetables, legumes, nuts, seeds, unrefined grains, and fish.
The mineral zinc is a constituent of the hydroxyapatite mineral crystals of bone, and plays a role in the regulation of bone turnover. Zinc is also needed for the correct functioning of alkaline phosphatase, which is required for bone mineralization. Mild degrees of zinc deficiency have been reported in the elderly and could potentially contribute to poor bone status. Lean red meat and meat products, poultry, whole grain cereals, pulses and legumes are good sources of zinc.
These are but a few nutrients that are important in maintaining bone health.
Good nutrition alone will neither prevent nor cure osteoporosis, but in the context of a bone friendly lifestyle (exercise, stop smoking, limit alcohol intake) it is probably the more pleasurable and less onerous task on the list!