High magnesium intake and calcium supplementation has been associated with low risk of colorectal cancer, but calcium is believed to prevent the body from absorbing magnesium.
Dr Qi Dai, assistant professor of medicine at Vanderbilt University, says that calcium can protect against colorectal cancer only in the presence of magnesium.
"If calcium levels were involved alone, you'd expect the opposite direction. There may be something about these two factors combined - the ratio of one to the other - that might be at play", said Qi Dai.
The researchers found that supplementation of calcium only reduced the risk of adenoma recurrence if the ratio of calcium to magnesium was low, and remained low during treatment.
"The risk of colorectal cancer adenoma recurrence was reduced by 32 percent among those with baseline calcium to magnesium ratio below the median in comparison to no reduction for those above the median," said Qi.
The research team suggest that designing a personalized diet/supplementation regimen may be better than supplementing with one or the other alone.