Women with a high intake of calcium from their diet and supplements could be at higher risk of dying from heart disease, a Swedish study suggests.
When researchers followed 61,443 Swedish women for an average of 19 years, they found nearly 12,000 deaths, including nearly 4,000 from cardiovascular disease and almost 1,900 from ischemic heart disease.
"High intakes of calcium in women are associated with higher death rates from all causes and cardiovascular disease but not from stroke," Dr. Karl Michaelsson, a clinical professor in the department of orthopedic surgical sciences at Uppsala University and co-authors concluded in this week's issue of the British Medical Journal.
In the study, the average intake in for those consuming the lowest amounts of calcium was 572 milligram a day, the equivalent of five slices of cheese, and in the highest 2,137 milligrams per day.
Women taking calcium tablets with a dietary intake above 1,400 milligrams per day were 1.5 times as likely to die from cardiovascular disease than those getting 600 to 999 milligrams a day.
The death rate from cardiovascular disease in the group with the highest calcium intake was 4.0 per 1000 person years while the death rate in the group with the lower calcium intake was 3.5 per 1000 person years. Person years describes the number of people, times the number of years exposed.
Diets with very low or very high levels of calcium can override normal controls and cause changes in the blood levels of calcium or related hormones, the researchers said.
The findings come on the heels of three recent reanalyses of randomized trials in women pointing to a higher risk of ischemic heart disease and stroke with calcium supplements. That was not found in a fourth randomized trial.
"Many older adults increase dietary intake of calcium or take calcium supplements to prevent bone loss and there had been speculation that increased calcium intake with or without vitamin D could improve cardiovascular health," Dr. Gregg Fonarow, an American Heart Association spokesman who wasn't involved in the study, told HealthDay News.
Osteoporosis Canada recommends getting about 1,200 milligrams every day of calcium, preferably from diet. One glass of milk has about 300 milligrams of calcium.
Taylor Wallace, a representative of the supplement industry, said the original Swedish mammography study was not set up to address the question it answered.
"It did not adjust for the role of hormone replacement therapy (HRT), and since science has gone back and forth as to whether HRT helps or hurts the heart, the jury is out as to how this might influence the findings," Wallace said in a statement on the Council for Responsible Nutrition's website.
No cause and effect relationships can be drawn from the study, which was funded by the Swedish Research Council.