Taking calcium supplements may double the risk of dying from cancer, a new study suggests.
Analysis of the medical records of 27,000 adults found links between high doses and cancer in later years.
However, no link was found between increased consumption of foods containing calcium and the disease.
Meanwhile certain other nutrients in food – but not supplements – were generally linked to a lower risk of all-cause and cancer death.
Scientists writing in the journal Annals of Internal Medicine said cancer patients could be putting themselves in greater danger by taking calcium supplement doses higher than 1,000 milligrams per day.
The found that after more than 12 years’ follow-up there were roughly 24 cancer-related deaths per 1,000 person-years compared to 12 in nonusers.
Up to 5 million people in the UK take calcium and vitamin D supplements in an attempt to avoid osteoporosis in later life.
Lead scientist Dr Fang Fang Zhang, from Tufts University, said: “It is important to understand the role that the nutrient and its source might play in health outcomes, particularly if the effect might not be beneficial.
“Our results support the idea that, while supplement use contributes to an increased level of total nutrient intake, there are beneficial associations with nutrients from foods that aren’t seen with supplements.
“This study also confirms the importance of identifying the nutrient source when evaluating mortality outcomes.”
The scientists compared the intake of a range of nutrients with rates of death from all causes, cardiovascular disease, and cancer.
They showed that adequate consumption of vitamins A and K, as well as magnesium and zinc, reduced the risk of death.
But this finding only applied to nutrients in food, not supplements.
High levels of calcium intake through supplements was associated with a greater risk of death from cancer.
In addition, there was evidence that unnecessary consumption of vitamin D supplements by individuals who were not deficient in the vitamin might increase the risk of death from any cause.