According to the study, published this month in the American Journal of Clinical Nutrition , women who eat chocolate daily have an overall bone density 3.1 per cent lower than those who consume it less than once a week.
The findings will surely come as a blow to the positive image of dark chocolate, often feted for having its heart-healthy properties.
"Cocoa and chocolate have been promoted as having a range of beneficial cardiovascular properties," said head researcher Jonathan Hodgson, from the University of Western Australia .
"But the effect of chocolate intake on other organ systems has not been studied."
For the study, 1,001 women aged 70 - 85 were randomly assigned either oral calcium supplements or a matched placebo for a period of several weeks.
During this period they were also asked to keep a dairy of how often they consumed chocolate or cocoa-based drinks.
The researchers did no distinguish between types of chocolate consumed.
At the end of the allotted time Hodgson and his colleagues measured the whole-body and regional bone density and strengh of each participant using X-rays.
The researchers found that the women who ate chocolate less than once a week had significantly stronger bones than those who consumed the treat on a daily basis, with calcium supplementation having little effect on the results.
"Additional studies are needed to confirm these observations, but confirmation of these findings could have important implications for prevention of osteoporotic fracture," the scientists said.
Hodgson suggests even though chocolate contains flavonols and calcium, both linked to having a positive effect on bone density, the confectionery product also contains oxalate, an inhibitor of calcium absorption, and sugar, linked to calcium excretion.
The study comes less than a month after British medical journal the Lancet warned against viewing chocolate as a health food, saying that consumers are generally unaware that manufacturers remove the healthy element - the flavanols.
Bridget Aisbett, spokesperson from the British Nutrition Foundation, agreed that information over how healthy chocolate actually is should always be treated with a degree of caution.
"There has been a lot of scientific research into the health properties of chocolate - both for and against, and so consumers should not regard it as health food, but rather as an occasional treat," she told ConfectioneryNews.com.
Source: American Journal of Clinical Nutrition Authors: J. M. Hodgson and others