Taking excessive calcium tablets may increase the risk of cancer, according to scientists who say that getting adequate nutrients from food sources is more beneficial than consuming supplements.

The study, published in the journal Annals of Internal Medicine, also showed that adequate intake of certain nutrients reduces risk of death from any cause, when nutrient source is foods, but not supplements.

Researchers found that supplemental doses of calcium exceeding 1,000 miligrammes per day is linked to an increased risk of cancer death,

"As potential benefits and harms of supplement use continue to be studied, some studies have found associations between excess nutrient intake and adverse outcomes, including increased risk of certain cancers," said Fang Fang Zhang, associate professor at Tufts University in the US.

"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," Zhang said.

The study used data from more than 27,000 US adults ages 20 and older to evaluate the association between dietary supplement use and death from all causes, cardiovascular disease (CVD), and cancer.

The researchers assessed whether adequate or excess nutrient intake was associated with death and whether intake from food versus supplement sources had any effect on the associations.

The researchers found that adequate intakes of vitamin K and magnesium were associated with a lower risk of death, while adequate intakes of vitamin A, vitamin K, and zinc were associated with a lower risk of death from CVD.   Excess intake of calcium was associated with higher risk of death from cancer, they said.

When sources of nutrient intake were evaluated, the researchers found that lower risk of death associated with adequate nutrient intakes was limited to nutrients from foods, not from supplements.

In addition, the researchers found that dietary supplements had no effect on the risk of death in individuals with low nutrient intake.

Instead, the team found indications that use of vitamin D supplements by individuals with no sign of vitamin D deficiency may be associated with an increased risk of death from all causes including cancer. Further research on this potential connection is needed.

"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," said Zhang.