by Playfuls Staff |
16th February 2006
Calcium and vitamin D supplements in healthy postmenopausal women provide a modest benefit in preserving bone mass and prevent hip fractures in certain groups including older women but do not prevent other types of fractures or colorectal cancer, according to the results of a major clinical trial, [more] part of the Women's Health Initiative (WHI). While generally well tolerated, the supplements were associated with an increased risk of kidney stones.
The study results are published in the February 16 issue of The New England Journal of Medicine. The WHI is sponsored by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health.
The WHI Calcium with Vitamin D (CaD) trial of 36,282 postmenopausal women ages 50 to 79 found a small but significant 1 percent higher hip bone density for those taking calcium combined with vitamin D compared to those taking placebo. During the trial, 374 women had hip fractures with a fracture rate of 14 per 10,000 cases per year in the supplemented group compared to 16 per 10,000 per year in the placebo group. This 12 percent reduction in hip fracture in those taking the calcium plus vitamin D supplement was not statistically significant; however, women who consistently took the full supplement dose experienced a significant 29 percent decrease in hip fracture. Women older than 60 had a significant 21 percent reduction in hip fracture. The supplements had no significant effect on spine or total fractures.
Calcium/vitamin D supplements provided no detectable effect on the incidence of colorectal cancer. There were similar rates of cancer in both the calcium/vitamin D and placebo groups (13 cases per 10,000/year compared to 12 cases per 10,000/year respectively).
Overall, the supplements were well tolerated by participants and the only adverse effect found was a 17 percent increase in kidney stones. Kidney stones were reported by 449 women (34 cases per 10,000 per year) in the CaD group compared to 381 women (29 cases per 10,000 per year) in the placebo group.
The WHI Calcium with Vitamin D trial was primarily designed to study the effect of calcium/vitamin D supplementation on preventing hip fracture with secondary study objectives testing the effect of CaD on spine and other types of fracture and on colorectal cancer. Participants in this study had previously enrolled in one or both of the WHI trials of hormone therapy or dietary modification.
Half of the over 36,000 participants in the CaD trial received a daily dose of 1000 milligrams of calcium carbonate combined with 400 IUs of vitamin D3. The other half of the study group received placebo pills in similarly marked bottles. Participants could choose between chewable or swallowable pills. During the study, a sub-set of participants had regular bone density scans. Study participants were followed for an average of 7 years with three-quarters of them still taking their pills by the end of the study.
Osteoporosis, a skeletal disorder characterized by weakened bones leading to an increased risk of fracture is a major cause of disability, loss of independence, and death. It contributes to an estimated 300,000 hip fractures in the U.S. each year. Four out of 10 women over 50 will experience a fracture at the hip, spine, or wrist in their lifetime. Ten million people in the U.S. are estimated to have osteoporosis and 34 million more have low bone mass, placing them at greater risk for fracture.
According to the study's authors, there are several possible reasons why despite improvements in hip bone density, the reduction in hip fractures was smaller than expected and only statistically significant in certain groups – those over 60 and women who took the full intended dose of combined supplements.
The rate of hip fractures was about half of what was expected, and this decreased study power to show a significant finding, according to Dr. Jackson.
The study found no evidence of benefit from calcium/vitamin D for the prevention of colorectal cancer, according to Jean Wactawski-Wende, Ph.D., epidemiologist and the study's lead investigator at the University at Buffalo.
Over an average of 7 years, 322 women in the study were diagnosed with invasive colorectal cancer. There was no statistically significant difference between the two groups in number of cancer cases or in the characteristics or severity of tumors. There were also no differences between groups in the number of polyps reported by the participants. When the investigators analyzed only the data obtained from participants who were taking most of their study pills, there was still no benefit seen from calcium/vitamin D supplementation.
