If you are a woman over forty, you may be starting to worry about bone health. Everyone loses bone as they age. By the time a women is told she has osteoporosis, her gradual loss of bone mass has been progressing for years. Men lose bone too, but only about half as fast as women. Medically speaking, osteoporosis is characterized by low bone density and structural deterioration of bone tissue.(1) The soft spongy bone in the wrists, hips, and spine are the most vulnerable to osteoporosis and prone to breakage as a result.

Fractures due to osteoporosis are a major health problem in industrialized nations. In the United States, approximately 150,000 hip fractures occur annually in women over age 65, sentencing many women to long-term stays in nursing homes.(2) These fractures can be fatal. By age 80, some 40 percent of all women will have a spinal compression fracture and suffer with back pain, loss of height, and disability.(3)

Unlike the dead, brittle skeleton hanging in the high school biology lab, bone is a living, metabolically active tissue. Throughout life, bone is constantly rebuilding itself. Bone serves as a storehouse for minerals, chiefly calcium, which can be tapped to meet the body's mineral requirements. Bone is broken down through a process called “resorption,” releasing its minerals into the general circulation. New bone is then formed to replace the reabsorbed bone, preventing a net loss of bone. This is called bone “remodeling.” As we age, however, bone formation begins to fall behind, causing the gradual bone loss that culminates in osteoporosis.

Exactly why and how bone loss accelerates with aging is not completely understood. Many different physiologic changes appear to be involved.(4) Bone cells called “osteoblasts” that rebuild bone seem to falter with aging. Hormones of the thyroid and parathyroid glands control the movement of calcium in and out of bone: calcitonin secreted by the thyroid deposits calcium into bone while PTH from the parathyroids pull calcium out. As we age, calcitonin levels tend to fall coupled with a rise in PTH, tipping the scale toward bone breakdown.(5, 6) Estrogen protects against bone loss and declining estrogen levels after menopause increase bone resorption. Add in the reduced absorption of dietary calcium that comes with aging and we have a constellation of interwoven factors favoring bone loss.(7, 8)

While a certain amount of bone loss seems inevitable with the passage of time, the process is not entirely beyond our control. Dietary and lifestyle measures can, to some degree, help maintain bone health. Poor nutrition and other health habits such as smoking, alcohol abuse, and physical inactivity contribute to bone loss. Exercise, especially through activities like walking that put pressure on the weight-bearing bones, stimulates bone remodeling. Exposure to sunlight is helpful. Sunlight forms vitamin D in the skin, vitamin D in turn increases calcium absorption.

The risk of osteoporosis has been associated with heavy caffeine consumption. One study found that more than two cups of coffee or four cups of tea a day increased calcium excretion in the urine and the incidence of hip fractures.(9) Too much phosphorus in the diet favors bone loss by increasing excretion of both calcium and magnesium. High phosphorus foods such as animal protein and soft drinks should be consumed in moderation. In addition, older women with low blood levels of vitamin B12 had greater bone mineral loss.(10)

Milk drinking is commonly believed to promote strong healthy bones, but recent studies have raised questions about this. A Japanese study demonstrated that supplementing with calcium (200mg oyster shell with seaweed) more effectively suppressed parathyroid hormone th