FUNCTION: Bones give our bodies shape, act as levers against which our muscles work and serve as reservoirs for calcium needed in other parts of our body. As such, bones must be kept strong and resupplied with calcium over our entire life through a calcium-rich diet.

FORM: Human bones are strong but relatively light. Bones are made up of a compact outer layer and a more porous inner area. This inner area is commonly described as spongy bone because it is made up of a network of canals ringed by bone cells with spaces in between. The outer layer is what makes bones strong, while the inner layer serves to keep them relatively light. Bones contain both living tissue and minerals, mainly calcium and phosphate; they are alive, changing with our body over time and undergoing continuous remodeling throughout life. Calcium and phosphate must be part of a healthy diet in order to keep bones strong.

BONE MASS: Bone mass is the total amount of bone in a body. A person's bone mass depends on sex, race, nutrition, exercise and overall health, and peaks sometime during the third decade of life. Continued calcium intake throughout life and exercise maintain and build bone mass.

BONE LOSS: Bone loss refers to the decline of bone mass after its peak, which for most people comes after the age of 30. Bones lose both mineral and living tissue. Though a certain amount of bone loss is a normal part of natural aging, life habits (such as smoking and drinking), diseases and space flight can accelerate bone loss and result in an increased susceptibility to fracture. We strengthen our bones with vitamins and minerals, the most important of which are vitamin D and the mineral calcium. Vitamins and minerals come from the food we eat.

VITAMINS: Vitamins are organic compounds required for regulation of metabolism and the healthy growth and functioning of the body. They can be loosely organized into two categories:

WATER SOLUBLE: Water-soluble vitamins travel through your bloodstream. Because the body does not store these vitamins, your body only uses what it needs, and they need to be replaced often. Watersoluble vitamins include vitamin C, thiamin (B1), riboflavin (B2), cobalamine (B12), pyridoxine (B6), niacin, folic acid, biotin and pantothenic acid.

FAT SOLUBLE: Fat-soluble vitamins are stored in the fat tissue and liver of your body. They remain in your body fat and are used as your body needs them. Fat-soluble vitamins include vitamins A, D, E, and K.

MINERALS: Minerals are inorganic compounds that fall into two categories, macrominerals and trace minerals.

MACROMINERALS: Your body needs large amounts of macrominerals, which include calcium, phosphorous, magnesium, sodium, potassium, chloride, and sulfur.

TRACE MINERALS: The body requires only a small amount of trace minerals, which include iron, manganese, copper, iodine, zinc, cobalt, fluoride, and selenium. Calcium is a mineral that helps maintain bone. Foods that are rich in this important dietary requirement include milk, cheese, broccoli, cauliflower, and calcium-fortified foods.

OSTEOPOROSIS
A healthy diet provides active bones with the raw materials they need to stay strong and healthy. Exercise causes bones to use more calcium and increases skeletal mass. If any part of this cycle breaks down, bone loss is more likely to occur. Vitamin D enables the body to use and absorb calcium and phosphorus. This vitamin is essential for the body to make use of available minerals. Weight-bearing activities, such as brisk walking, stair climbing, hiking and dancing, put weight on the bones and help increase skeletal mass.

Women have approximately 30 percent less bone mass than men at peak. Bone loss in women increases rapidly after menopause due to a reduction in estrogen production. Among those who live to be 90, 32 percent of women and 17 percent of men will fracture their hip, mostly due to osteoporosis.

HOW MUCH CALCIUM DO YOU NEED EVERY DAY?
At this life stage, you need this much calcium:

child (age 1 to 10) = 800 milligrams
young adult (age 11 to29) = 1,200 milligrams
adult (age 30 to 50) = 1,000 milligrams
adult (age 51 to 64)* = 1,200 milligrams
adult (age 65 and over)** = 1,500 milligrams
* also includes pregnant and lactating females and postmenopausal females on estrogen
** also includes postmenopausal females not taking estrogen

Nearly half of postmenopausal American women do not know their bone-mineral density (BMD) is low according to the National Osteoporosis Risk Assessment (NORA) study. When you have low BMD, you are more at risk of bone fracture. Based on the studyís results, lead investigator Dr. Ethel S. Siris and colleagues concluded that healthcare providers should pay more attention to identifying and managing osteoporosis in order to prevent future fractures.

The researchers examined more than 200,000 women from 34 states over a 2-year period in the largest research study of osteoporosis ever conducted among postmenopausal American women. None of the women in the study had ever been diagnosed with osteoporosis in the past, and all could walk.

The researchers also found the following:

The likelihood of developing osteoporosis increases with age. About 7% of study participants with low BMD also had osteoporosis.

According to the study, certain women are at greater risk of osteoporosis, including:

- Women of Asian or Hispanic descent
- Smokers
- Those who use cortisone medications
- Those with a personal or family history of fractures
- Women with a significantly lower risk of developing osteoporosis include:Women of African-American descent
- Users of estrogen or diuretic medications
- Those who exercise regularly
- Those who consume alcohol
- Women with a higher body mass index

NORA was funded and managed in large part by Merck & Co., Inc, manufacturer of a medication used to treat and prevent osteoporosis in postmenopausal women.

Journal of the American Medical Association. 2001;286:2815-2822.

American Journal of Epidemiology. 2002;155:72-79.