A new study finds higher levels of vitamin E(Drug information on vitamin e) consumption could stave off liver cancer. The study, aiming to assess link between dietary habits and liver cancer incidence, followed 132,837 men and women for an average of at least 5 years and is published in the Journal of the National Cancer Institute. All of the participants were from China.
Vitamin E intake from food and from supplements was inversely associated with liver cancer risk (P = .01). The association held up for those who had a family history of liver disease and those who self-reported liver disease. Among the participants, 267 cases of liver cancer were reported—118 women and 149 men. The data was not statistically significant when only the male cohort data was analyzed. However, as there is no current evidence for sex-based difference of vitamin E metabolism, the authors attribute the result to “random fluctuation” and the relatively few liver cancer cases reported in the study.
“Our finding is consistent with the biological properties of vitamin E and experimental results,” said Xiao-Ou Shu, MD, PhD, of the Vanderbilt Epidemiology Center in Nashville, Tennessee and one of the lead authors of the study.
“The vitamin E and liver cancer association was seen for subjects with and without liver diseases in our study, suggesting that the effect of vitamin E do not restrict to a particular type of liver cancer, such as the one caused by the hepatitis B virus,” said Shu. “Thus, the finding of our study should be able to be generalized to other populations.”
Shu cautioned that a more definitive answer can only be obtained when the American Chinese and the general US population are further studied.
The study also found that vitamin C supplements (but not dietary vitamin C) and multivitamin supplements were associated with an increased risk of liver cancer among those participants who either had self-reported liver disease or had a family history of liver cancer. It should be noted that the statistical power for this analysis was low due to the smaller sample size. Additionally, those participants with liver disease or a family history of liver cancer were more likely to take vitamin supplements, therefore a reverse causation is possible, highlight the authors.
The study found no association of vitamin B or calcium intake and risk of liver cancer.
The participants who developed liver cancer tended to be older, to have a lower education, a family history of liver cancer, and a history of viral hepatitis compared to those who remained without cancer during the study follow-up. Women with liver cancer were more likely to have a higher body mass index while men were more likely to have a history of diabetes, a higher fat intake, and a lower family income. Neither smoking nor drinking habits differed among those who developed liver cancer and those who did not have liver cancer during the study.
Liver cancer is the third most common cause of cancer mortality worldwide. More than half of all liver cancers occur in China. It is the fifth most common cancer in men and the seventh most common in women according to the International Agency for Research on Cancer. Among the known risk factors are hepatitis B and hepatitis C infections as well as chronic alcohol(Drug information on alcohol) consumption and aflatoxin. A prevalent hypothesis of liver carcinogenesis is the chronic DNA damage from perpetual inflammation, which can promote cancer cell growth.
“The contribution of genetic factors to liver cancer has not been well investigated and is likely to play an important role,” said Shu. “In my opinion, environmental factors are the main driving force behind the high incidence of liver cancer among Asians,” Shu added.
Study Design and Results
Vitamin E intake from both diet and supplements was assessed among those enrolled in the Shanghai Women’s Health Study and the Shanghai Men’s Health Study. The participants filled out food questionnaires that were followed up by in-person interviews.
The two cohorts were studied by both Vanderbilt University and the Shanghai Cancer Institute. The participants were enrolled for 3 years starting in 1997 and followed until 2006. The men’s cohort was followed up for an average of 5.5 years and the women’s cohort for an average of 10.9 years. All participants were between 40 and 74 years of age at recruitment.
Vitamin E and A, zinc, copper, and selenium(Drug information on selenium) in the diet are thought to reduce liver cancer rates by reducing hepatitis infections. Vitamin E has been previously shown to improve liver function in patients with a viral hepatitis infection, according to the authors. However, compared to the current study, the only studies assessing liver cancer and dietary intake were small, retrospective cohort studies.
A recent study showed vitamin E supplements do not prevent prostate cancer and may actually increase its incidence. “The etiology for cancers differs greatly from cancer to cancer, and sometimes across subtypes of a same cancer. Therefore, it is not uncommon that a factor protects one type of cancer but not another type of cancer,” said Shu. Additionally, the current study participants got vitamin E mainly from the diet without ingesting higher levels of vitamin E from supplements. The effect of vitamin E can differ depending on which of the eight types is ingested and which population is studied.
In their discussion, the authors point out that because fewer than 17.5% of study participants took vitamin supplements and because food in China is not fortified with vitamins and minerals, the Chinese population is a unique way to study dietary influences on disease outcomes. The authors plan to further investigate the role of vitamin E intake on liver cancer risk by measuring the blood levels of vitamin E and markers of hepatitis B infection. “We would also like to explore the role of genetic factors in this association,” said Shu.
What are excellent sources of dietary vitamin E? Rich vitamin E foods include spinach, Swiss chard, peppers, and other dark green vegetables, almonds, sunflower seeds and other nuts, tropical fruits, and vegetable oil. “Personally, I would prefer to get my vitamin E from diet instead of supplements, as many vitamin E rich foods also contains other nutrients and phytochemicals that are beneficial to health,” said Shu.