Osteoporosis is a disease in which the bones in our body thin so much that even a minor injury can cause a fracture. Simply lifting a heavy bag of groceries out of the trunk of the car can cause a spine fracture in a person with osteoporosis. Osteoporosis is a "silent" disease until a fracture occurs. Thinning bones do not hurt until they break. Our skeletons are living tissue and our bodies are constantly building new bone and removing old and damaged bone tissue from our skeleton. As we age, and particularly in women after menopause, more bone is broken down than is replaced, leading to a net loss of bone. This causes thinning of the bones, so called osteopenia.
Osteoporosis and osteopenia are very common problems and affect almost 44 million Americans over the age of 50, most of whom are women. This number is expected to grow to 52 million by 2010. While new drugs to prevent bone loss and treat osteoporosis are being developed, these drugs are expensive and can have significant side effects. It is clear that we need other approaches to help maintain bone health. Since bone is living tissue, it makes perfect sense that nutrition is very important to skeletal health. Despite this, a detailed understanding of how nutrition influences the skeleton is still lacking for many nutrients. Two of the most intensively studied nutrients are calcium and vitamin D. It is very clear now that adequate amounts of both are important for slowing the rate of bone loss as we age and reducing the risk of fractures.
One of the dietary factors that traditionally had not been thought to be good for skeletal health is dietary protein. It had been thought that dietary protein leached calcium from the skeleton and caused thinning of the bones. Many scientists still believe this because when dietary protein intake increases, the amount of calcium in the urine goes up. It has been assumed that this extra calcium in the urine was coming from your bones.
Ten years ago our research group at Yale University and the University of Connecticut, began investigating the effect of dietary protein on bone health. To our surprise, we found that dietary protein causes a significant improvement in the efficiency with which our body absorbs calcium from the diet. When we increased dietary protein intake from low-normal (0.7 grams of protein per kilogram of body weight per day) to high normal (2.1 grams of protein per kilogram of body weight per day) the ability of the body to absorb calcium from the diet improved by more than 35%. We also found that the rate at which the skeleton was being broken down was not increased by the increase in dietary protein. Finally, we found that the increase in urine calcium that had troubled other investigators was caused by the increase in calcium absorption from the intestinal tract. The body was getting rid of some of the extra calcium it had absorbed through the urine. It was not due to bone breakdown at all.
Another research group from the University of North Dakota has recently reported similar findings as ours. They also found that increasing dietary protein was not bad for bones but actually helped bones hang on to calcium, particularly when the level of dietary calcium was low. Another report from the Framingham Osteoporosis Study has shown that in both men and women, a higher level of dietary protein was associated with better bone mineral density and a slower rate of bone loss with aging.
Despite what one might think, there are actually a large number of women and men in the U.S who consume a low protein diet on a daily basis. Between 32% and 41% of women over the age of 60 years consume a diet that contains less than the recommended dietary allowance for protein (0.8 grams/kilogram of body weight per day). It is important to realize that increasing dietary protein does not mean a person necessarily has to eat more fat. Skim milk, fish, egg whites and soy are all examples of sources of low fat, high quality protein.
Although our work suggests that dietary protein may be helpful in preventing bone loss in individuals who are consuming a low level of dietary protein, the only way to prove this is to do a scientific controlled study. We are currently conducting a multi-center trial, funded by the National Institutes of Health, to determine the effect of a natural protein supplement on bone health in women over the age of 60 and men over 70 who have low levels of dietary protein intake and thin bones. Help us find alternative, safe and effective therapies for the prevention of osteoporosis! See our advertisement about the SPOON Study on the opposite page.
Karl L. Insogna, M.D. received his medical degree from the University of Connecticut. He joined the faculty at Yale in 1984 and is currently a Professor in Medicine in the Department of Internal Medicine at Yale University. He is the Director of the Yale Bone Center, an integrated multispecialty clinical service that provides care to patients with osteoporosis and other metabolic skeletal disorders. He is also the director of the NIH-funded Yale Core Center for Musculoskeletal Disorders. Dr. Insogna is an internationally recognized expert in the field of metabolic bone diseases and has published widely on the topic in the field’s leading scientific journals. His current clinical research focus is on the impact of dietary protein on bone health.