The majority of women today are aware that calcium is essential in preventing osteoporosis, especially after the menopause.
Osteoporosis is a disease which causes progressive bone loss and fractures and it affects millions of Americans.
A preliminary study has found that when it comes to maintaining strong bones after the menopause, women may be better off eating plenty of calcium-rich food rather than relying on supplements for their intake of the mineral.
The researchers at Washington University School of Medicine say though their study is not definitive, dietary calcium may be better at protecting bone health than calcium which comes mainly from tablets.
They say this proved to be true even though the supplement-takers had higher average levels of calcium.
The study's lead author, Dr. Reina Armamento-Villareal says calcium from dietary sources is generally better absorbed than that from supplements, which could help explain the difference.
Dr. Armamento-Villareal, a bone specialist and assistant professor in the School of Medicine's division of bone and mineral diseases, says those getting calcium from foods also had more estrogen in their bodies which is needed to maintain bone mineral density.
As yet the food-estrogen connection remains unclear but the research says Armamento-Villareal is preliminary and offers a hypothesis to test.
For the research 183 postmenopausal women were asked to carefully log their diet and their calcium supplement intake for seven days; their bone mineral density and their urine for levels of estrogen were then tested.
The women were then split into three groups: those who got at least 70 percent of their daily calcium from supplements, those who got the same amount from dairy products and other food, and those whose calcium-source percentages fell somewhere in between.