Whole grains lower the risk of heart disease, but not that of cancer, a US study says.

People who eat more whole grains are more likely to live longer and avoid heart disease, but such a diet does not affect the risk of dying from cancer, a US study says.

The findings by researchers at Harvard University appear in the Journal of the American Medical Association (JAMA) Internal Medicine on Monday.

Scientists examined the records of more than 74,000 women and nearly 44,000 men from the mid-1980s until 2010.

They found that the more whole grains people reported eating, the lower risk they had of dying, particularly from heart disease, after adjusting for factors such as age, smoking and body mass index.

Every serving (28 grams per day) of whole grains - such as brown rice, oatmeal, whole wheat bread and pasta - was associated with five per cent lower mortality, and a nine per cent lower risk of dying from heart disease.

However, eating more whole grains did not make cancer deaths any less likely.

"These findings further support current dietary guidelines that recommend increasing whole grain consumption to facilitate primary and secondary prevention of chronic disease and also provide promising evidence that suggests a diet enriched with whole grains may confer benefits toward extended life expectancy," the study said.