Dairy Product, Calcium Intake and Lung Cancer Risk: A Systematic Review with Meta-Analysis

Important components of our diet, dairy products provide a variety of nutrients for humankind, and their effects on human health have been the target of research investigations for years. Milk was once believed to be quite healthy and was recommended strongly in dietary guidelines worldwide. However, concerns regarding the side effects of dairy products on human health have also existed for some time, a recent large cohort study reported that higher milk intake even increased the incidence of fracture and overall mortality, which aroused an intense debate regarding the consumption of milk products1. Considering the diverse effects of dairy products, the connection between dairy intake and specific diseases, especially cancer is a topic worth studying. Previous studies have reported inconsistent results with different cancers. For instance, studies showed that milk and calcium intake might protect against colorectal cancer2, but was associated with increased risk of prostate3 and ovarian cancers4, while no significant association was observed for pancreatic5, gastric6 and bladder cancers7. An important element in milk, calcium plays a crucial role in the biological effects of dairy products and has been found to be associated with the risk for certain malignant tumors2,8. As one of most common cancers in both the males and females, lung cancer is the leading cause of cancer-related death worldwide9. The primary risk factor for lung cancer is smoking, and accounts for ~80% of the cases in men and ~50% in women. Other risk factors associated with lung cancer include air pollution, cooking fumes, radon and asbestos exposure10,11. Growing evidence suggests that nutritional factors possibly may play a role in lung cancer development12,13. Over the past few decades, there have been many studies focused on the association between dairy consumption and lung cancer risk, however, the relationship is still unclear, as the evidence from these studies is scattered and unconvincing. Along with the arrival of the era of evidence-based medicine, it is necessary to collect previous data and summarize the results to make a quantitative conclusion. Therefore, we conducted a meta-analysis of observational studies to clarify the association between the intake of dairy products and calcium with lung cancer risk.