By Dr Sharan Sharma

Lung cancer is the leading cause of cancer mortality worldwide. Despite huge progress in the diagnosis and treatment of lung cancer, the 5-year survival rate for the disease is still about 15%. Although cigarette smoking remains a leading cause of lung cancer there are many other causes which are not well established yet. For example only a fraction of smokers develop lung cancer and a lot of lung cancers occur in people who have never smoked. Researchers have long suspected that diet be connected with this.

In the current issue of Cancer Epidemiology, Biomarkers and Prevention, researchers from National Cancer Institute, USA used data from the NIH-American Association of Retired Persons Diet and Health study of 482,875 subjects (288,257 men and 194,618 women) who were cancer-free and completed a food frequency questionnaire at enrolment between 1995 and 2003. They then used Cox proportional hazards models to estimate the relative risk adjusted for potential confounders.

During the mean follow-up of 7 years, from 1995 to 2003, a total of 7,052 lung cancer cases were identified (4,520 in men and 2,532 in women). Of the 7,052 lung cancer cases, 2,579 (37%) were adenocarcinomas, 1,246 (18%) were squamous cell carcinomas, 953 (14%) were small cell carcinomas, and 400 (6%) were undifferentiated carcinomas. The mean total (diet + supplement) intake was as follows: Ca, 1,002 mg/d; Mg, 374 mg/d; Fe, 24 mg/d; Cu, 2.32 mg/d; Se, 102 mg/d; women, 89 mg/d); and Zn, 17.7 mg/d.

For all subjects, researchers observed no significant associations between total Ca, Mg, Fe, Cu, Se, and Zn intakes and lung cancer risk. Total Ca intake was protective (P trend < 0.05) for current smokers and subjects with adenocarcinomas. Total Mg intake increased risk (P trend < 0.05) in men and current smokers. Total Fe intake was inversely associated with risk in women (P trend < 0.01). For dietary minerals, Mg increased risk (P trend < 0.05) in all subjects, among men and current smokers. Increased dietary Ca intake reduced risk in women (P trend = 0.05). Dietary Fe decreased risk in all subjects and among women (P trend < 0.05). Mineral intake from supplements was not shown to affect lung cancer risk.

Citing their results the authors note that dietary mineral influences lung cancer risk but the influence depends on the types of mineral and patient subtypes. They think their study needs validation particularly because of the unexpected result that Mg increases lung cancer risk when several studies in the past have established Mg as a cancer protecting mineral.