This study found that smoking was associated with an increased risk of gastric cancer incidence and mortality, while not drinking was correlated with a stronger beneficial effect of garlic supplementation on gastric cancer prevention.
A secondary analysis of the Shandong Intervention Trial, published in JAMA Network Open, found that smoking was associated with an increased risk of gastric cancer incidence and mortality.
However, the findings also indicated that not drinking alcohol was correlated with a stronger beneficial effect of garlic supplementation on gastric cancer prevention.
“Given our ongoing efforts to promote precision prevention and control of [gastric cancer], it will be important to illuminate the effects of intervention strategies on subgroups based on lifestyle factors and to identify any effect modifications by lifestyle factors on [gastric cancer] prevention resulting from long-term nutritional supplementation,” the authors wrote.
The Shandong Intervention Trial was a masked, randomized, placebo-controlled trial that aimed to evaluate the effect of vitamin and garlic supplementations and Helicobacter pylori (H pylori) treatment on gastric cancer in a factorial design with 22.3 years of follow-up. The study took place in Linqu County, Shandong province, China, which is a high-risk area for gastric cancer.
Overall, the trial included 3365 individuals aged 35 to 64 years from 13 randomly selected villages who agreed to undergo gastroscopy. Participants were given vitamin and garlic supplementation for 7.3 years, H pyloritreatment for 2 weeks (among those with H pylori), or placebo.
The dual primary outcome measures were gastric cancer incidence and gastric cancer mortality. Researchers also assessed the progression of gastric lesions as a secondary outcome.
Of the total cohort, 1677 (49.8%) were randomized to receive active vitamin supplementation, with 1688 (50.2%) receiving placebo, and 1678 (49.9%) receiving active garlic supplementation, with 1687 (50.1%) receiving placebo. Moreover, 151 gastric cancer cases (4.5%) and 94 gastric cancer deaths (2.8%) were identified.
Smoking was correlated with an increased risk of gastric cancer incidence (odds ratio [OR], 1.72; 95% CI, 1.003-2.93) and mortality (hazard ratio [HR], 2.01; 95% CI, 1.01-3.98). However, smoking was not correlated with changes to the effects of vitamin or garlic supplementation.
“The increased exposure to potent carcinogens and N-nitroso compounds when smoking may partly help to explain the increased risk of [gastric cancer] among those who smoke,” the authors wrote.
The protective effect on gastric cancer mortality associated with garlic supplementation was seen only among participants not drinking alcohol (never drank alcohol: HR, 0.33; 95% CI, 0.15-0.75; ever drank alcohol: HR, 0.92; 95% CI, 0.55-1.54; P for interaction = 0.03). Even further, significant interactions were only observed among those with H pylori (never drank alcohol: HR, 0.31; 95% CI, 0.12-0.78; ever drank alcohol: HR, 0.91; 95% CI, 0.52-1.60; P for interaction = 0.04). No significant interactions were found between vitamin supplementation and lifestyle factors though.
“Although our study failed to find significant associations between alcohol intake and [gastric cancer] risk, alcohol intake may modify the effect of garlic supplementation, with the protective effect of garlic supplementation on [gastric cancer] mortality seen particularly among those who did not drink alcohol,” the authors wrote. “Considering that dysbiosis of microbiota could be induced by alcohol as well as garlic supplementation, it remains to be elucidated whether the exploration of microbial dysbiosis can help to explain the interaction between alcohol intake and garlic supplementation on [gastric cancer] risk.”
Notably, a greater preventive effect of vitamin supplementation was observed among participants with low fresh vegetable and fruit intake. Researchers explained that the micronutrients from fruits and vegetables may contribute to the protective effect for gastric mucosa by anti-inflammatory damage; however, in this study population, the significant interaction was only seen for gastric lesion progression, not for gastric cancer incidence or mortality. The investigators indicated that the reason for this was unclear.
Importantly, detailed information on lifestyle factors, such as the frequency and volume of alcohol intake, duration and pack-year of cigarette smoking, and information on specific diet, was not available, which prevented researchers from further evaluating lifestyle factors. Additionally, the investigators had no relevant data on lifestyle changes made during the follow-up period and were not able to examine updated lifestyle factors.
“Our findings provide new insights into lifestyle interventions for [gastric cancer] prevention, suggesting that mass [gastric cancer] prevention strategies may need to be tailored to population subgroups to maximize the potential beneficial effects,” the authors wrote.
Guo Y, Li Z, Zhang J, et al. Association Between Lifestyle Factors, Vitamin and Garlic Supplementation, and Gastric Cancer Outcomes. JAMA Network Open. doi:10.1001/jamanetworkopen.2020.6628.