THURSDAY, Nov. 15, 2001 (HealthDayNews) -- While another cup of morning java may give grandma the jolt of energy she needs, the benefits may not be worth the risks. A new study shows too much caffeine can weaken bones in older women.
Post-menopausal women who consumed more than 300 milligrams of caffeine daily (about three 6-ounce cups of American-brewed coffee) were far more likely to have lower bone mineral density -- a measurement of bone strength -- than women who consumed less, says a study in this month's American Journal of Clinical Nutrition.
"It's important to realize we're not just talking about coffee, but all forms of caffeine -- tea, soda, chocolate. When the total amount goes over a certain limit, the risk of bone loss increases," says study author Dr. J.C. Gallagher, director of the Bone Metabolism Unit at Creighton University in Nebraska.
While the idea that caffeine could speed bone loss is not new, Gallagher says a lack of scientific proof prompted the new study.
"We looked at 500 women over a period of three years, and we could see the relationship between caffeine and bone loss quite clearly," says Gallagher.
In addition, he says women who possessed a particular version of a vitamin D receptor (VDR) appeared to have even greater bone loss because of caffeine.
"The increase was significant -- at least several times more bone loss was experienced by these women when caffeine was consumed," says Gallagher. Vitamin D helps bones absorb calcium and signals the kidneys to retain calcium.
Good bone density reduces the risk of osteoporosis, a painful and potentially debilitating disorder that causes bones to thin, become brittle and break easily.
For nutritionist Samantha Heller, however, the relationship between caffeine and bone loss is not so cut and dried.
"Several studies have found little or no relationship between bone density and caffeine consumption. There are other studies that suggest differently," she says.
The only thing we really know for certain is that caffeine increases urinary excretion of calcium, a mineral necessary for bone health, she says. The new findings may indicate the effects of caffeine-related calcium loss more than any direct effect of caffeine on bone health, she says.
The study looked at the caffeine consumption of nearly 500 post-menopausal women, aged 66 to 75, over three years. Each woman took a calcium and a vitamin D supplement daily, while an additional 96 women only took a placebo.
At the start of the study, doctors took bone density measurements of the hip and spine and used complex genetic testing to determine the presence of a particular type of vitamin D receptor.
The women were then asked to keep a diary of caffeine consumption, including coffee, tea and other beverages.
After three years, the women were divided into two groups: those who consumed more than 300 milligrams of caffeine daily and those who consumed less. The two groups were then further divided according to whether they had the specific vitamin D receptor cells.
"When the measurements were taken again, we found that the women who consumed more than 300 milligrams of caffeine daily had a significantly greater loss in bone mineral density than those who consumed under 300 milligrams," says Gallagher. Those with a particular type of vitamin D receptor cells had an even greater loss when caffeine was consumed, he says.
The association between caffeine and bone loss prevailed even after researchers adjusted results for other factors linked to bone loss, including smoking, age, alcohol and calcium intake.
What To Do
In an editorial accompanying the study, Linda K. Massey of Washington State University, in Spokane, writes that until doctors can readily identify women who carry the genetic risk associated with vitamin D receptors, it's too soon to advise all women to avoid caffeine altogether. Instead, she suggests moderate caffeine intake with adequate calcium consumption.
Gallagher endorses that suggestion.
"As is often the case, moderation is the key here. If caffeine consumption is kept under 300 milligrams daily, a woman may have some protection against bone loss," he says.
Moderate caffeine consumption in terms of coffee is about 16 ounces daily. The suggested amount for tea, which contains less caffeine, is about 32 ounces daily.
And if you do consume a lot of caffeine, keep calcium intake high.
"Although peak bone mass is attained early on, a poor diet and lack of exercise can diminish the calcium stores we do have and increases our risk for osteoporosis," says Heller.
She says a woman's best defenses include eating lots of calcium-rich foods, such as low-fat dairy products and leafy green vegetables, and getting plenty of regular exercise.
For more information on bone health visit the National Osteoporosis Foundation.
To learn if you're getting enough calcium in your diet, check this Calcium Calculator.
For more on caffeine and a guide to caffeine content in common foods and beverages, visit The McKinley Health Center.
