For as long as low-fat diets have been advocated to lower serum cholesterol levels there have been critics claiming that reducing dietary fat could be harmful. One of the most persistent claims of those warning about the dangers of low-fat diets has been that lowering serum cholesterol levels may somehow promote cancer.

This claim has been fueled by numerous epidemiological studies showing lower serum cholesterol levels are indeed associated with an increased risk of developing at least several types of cancer. But epidemiological data showing a correlation between lower serum cholesterol levels and increased cancer risk do not prove this correlation is causal. Indeed, epidemiological data that excludes the first few years of follow-up has consistently shown that the correlation between lower serum cholesterol and increased cancer risk weakens significantly suggesting the correlation is due to reverse causation. Reverse causation would mean that some cancers apparently lower serum cholesterol well before they are diagnosed. ¹However, while the association between reduced serum cholesterol and cancer weakened over time it did not eliminate it even after 5 to 6 years of follow-up. Proponents of the "low cholesterol causes cancer" theorists suggested that perhaps reverse causation accounts for some but not all of the increased cancer risk due to lower cholesterol levels.Data from two new large long-term prospective clinical trials should end the debate about whether a lower serum cholesterol might promote cancer. One study followed 29,093 male smokers age 50-69 for 18 years. During the follow-up period 7,545 were diagnosed. The results showed that while a higher serum cholesterol appeared to reduce the risk of developing cancer it weakened over time and disappeared completely after 9 years. They conclude: "Our findings suggest that prior observations regarding serum total cholesterol and cancer are largely explained by reverse causation." ² In addition, this study did find a modest reduction in the risk of developing some cancers such as liver, lung, blood, and prostate cancers from a higher HDL level. The second study followed 5,586 men age 55 and older since the early 1990s. During the follow-up period 1,251 cases of prostate cancer were diagnosed. While there was no overall association between prostate cancer and serum cholesterol levels, the risk of developing an aggressive type of prostate cancer increased significantly in those with higher total cholesterol and LDL levels. ³Bottom Line: There no longer is any reason to suspect a lower serum cholesterol level might promote cancer. By James J. Kenney, PhD, RD, LD, FACN1.  Cancer Causes Control 1991;2:253-612.  Epidemiol Biomarkers Prev. 2009;18:2814-213.  Epidemiol Biomarkers Prev. 2009;18:2807-13