Diet and lung cancer 20+ years later: More questions than answers?

Abstract

A critical review of epidemiological studies on diet and lung cancer over the last 20+ years has not provided overwhelming evidence that higher consumption of vegetables, fruit, low-fat/low-cholesterol foods or such micronutrients as carotenoids, selenium and vitamins A, C or E is associated with reduced lung cancer risk. Results from case-control studies have been more positive, with about one half showing fruit and vegetables or their associated micronutrients to be associated with reduced risk. However, most results from cohort and serum micronutrient studies, which avoid the problems of inaccurate accounting of diet and recall bias, were statistically insignificant. Moreover, although most studies were conducted on white male smokers in North America and Europe, the few studies which found significant contrary trends were among subjects of different backgrounds, i.e., black American males and Chinese women in China. Since male smokers vs. nonsmokers in Europe, North America and Japan have been shown in other studies to be lower consumers of fruit/vegetables, and less likely to pursue "perceived healthier lifestyles," the possibility that some of the epidemiological findings on diet and lung cancer are artifactually due to inadequate adjustment for behavioral correlates of smoking and health seekers in a particular society must be considered. This is especially true with recent chemoprevention trials showing higher lung cancer incidence and deaths among consumers of beta-carotene supplements vs. placebo.

Dietary Habits and Risk of Lung Cancer Death in a Large‐scale Cohort Study (JACC Study) in Japan by Sex and Smoking Habit

“…discrepancy between the observation studies and intervention could be explained by the possibility that the excessive doses of β-carotene given in those intervention studies may be carcinogenic in vivo, and that the cooperative action of carotenoids and other compounds in fruits and vegetables is necessary to inhibit carcinogenesis. 1,[3][4][5][6][7] Recently, flavonoids in vegetables, which scavenge free radicals and are strongly antioxidative, have been added to the list of protective compounds. 24,25) A high intake of green-leafy vegetables, oranges and other fruits was, in our study, associated with a significant dose-dependent reduction in risk of lung cancer among males, and a high intake of the latter two was also associated among male current smokers.…”

“…This result was consistent with numerous previous studies. [1][2][3][4][5][6][7]14) However, significantly low HRs were not observed for the highest intake of carrots and squash, and tomatoes. Exposure misclassification may be larger among males than females because males do not usually cook themselves and cannot exactly evaluate their intake of those vegetables.…”

“…A high consumption of green-yellow vegetables or fruits has been believed to reduce the risk of lung cancer although some β-carotene intervention studies resulted in failure. [1][2][3][4][5][6][7] It is considered that experimental mutagenesis and carcinogenesis in animals could be inhibited by a large number of compounds from edible plants, including carotenoids, polyphenols, thiols, trace metals, terpenes, tocophenols, and degradation products of glucosinolates. 1) Recently, the protective activity of vegetables and fruits has been focused on antioxidative micronutrients such as carotenoids, vitamin C, folate and others, and recent studies have been focusing on the interactions among them.…”

“…1) Recently, the protective activity of vegetables and fruits has been focused on antioxidative micronutrients such as carotenoids, vitamin C, folate and others, and recent studies have been focusing on the interactions among them. [1][2][3][4][5][6][7][8] Some studies reported that the protective effect of vegetables and fruits was stronger among current smokers than among nonsmokers. [9][10][11] It is thought that antioxidants strongly reduce the oxidative stress due to smoking.…”

Sources of Vitamin A in the Diets of Pre-School Children in the Avon Longitudinal Study of Parents and Children (ALSPAC)

“…Deficiency can increase the likelihood of a range of diseases and is the main cause of blindness in children; an estimated 250,000–500,000 lose their sight worldwide each year [4]. In adults, some studies have found a link between diets low in beta-carotene and some cancers [5], e.g., a higher intake of green and yellow vegetables associated with a decreased risk of lung cancer [6]. However, other studies have been unable to show this protective effect [7].…”