Small amounts of iron and calcium in the diet or in the form of supplements may play an important role in the development of lung cancer, especially among smokers, a study suggests.

Iron, zinc, and calcium are micronutrients that participate in the metabolism of damaging forms of oxygen, known as reactive oxygen species. Intake of these micronutrients has been associated with higher risks of certain cancers, such as colorectal, breast, and prostate cancers.

“Some recent literature has associated these micronutrients with disease including cancer, but nobody had looked into it in the lung,” said Dr. David C. Christiani from Harvard School of Public Health and Harvard Medical School.

Christiani and his colleagues looked for associations between dietary iron, zinc, and calcium intake and the risk of lung cancer in 923 patients with lung cancer and 1125 healthy controls. To assess micronutrient intake, they used a 126-item food-frequency questionnaire that took into account potential risk factors such as smoking history.

When the team analyzed the 3 micronutrients separately, iron and calcium were associated with a higher risk of lung cancer but zinc was associated with a lower risk of lung cancer. However, the associations were stronger when all 3 micronutrients were analyzed in the same model.

“The associations hold true, no matter the source of the micronutrients,” Christiani said. “Iron and calcium in particular, both dietary and in supplements, are associated with increased risk of lung cancer.”

The investigators also found differences related to smoking history, with the effects being particularly strong in current smokers, and less so in former smokers.

“The message here for smokers and for former smokers is, don’t take large amounts of supplements, particularly those with iron or calcium, unless you have a medical indication for them,” warned Christiani. “People tend to take lots of vitamins and minerals thinking that they are good for them. We don’t recommend large dietary shifts until these results are confirmed in further studies.”

SOURCE: Epidemiology, November 2005.