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Smoking status, history increase incident NAFLD risk

Results from a recent study showed that current smoking habits and length of time smoking correlated with an increased risk for nonalcoholic fatty liver disease in both men and women.

“Given the rising prevalence of NAFLD and its hepatic and extrahepatic complications, it is important to identify modifiable risk factors and develop preventive strategies,” Hyun-Suk Jung, MD, from the Kangbuk Samsung Hospital in South Korea, and colleagues wrote. “Our study findings suggest that smoking is an independent risk factor for the development of NAFLD and may affect NAFLD progression adversely.”

The study comprised 199,468 participants who underwent comprehensive health examinations between Jan. 1, 2002, and Dec. 31, 2016, with at least one additional exam before Dec. 31, 2017. Mean age was 36.5 years in men and 36 years in women. Participants reported if they were current or former smokers with 37.1% of men and 94.5% of women reporting they never smoked.

During 1,070,991 person-years of follow-up, 45,409 participants developed NAFLD for an incidence rate of 42.4 per 1,000 person-years.

Compared with participants who never smoked, current smoking correlated significantly with an increased risk for NAFLD in both men (HR = 1.15; 95% CI, 1.12-1.18) and women (HR = 1.14; 95% CI, 1.03-1.27) after adjusting for age, BMI, alcohol intake, regular exercise, diabetes and hypertension, triglycerides, and cholesterol.

In multivariate analysis, the risk for incident NAFLD increased from 10 to 19.9 pack-years (HR = 1.25; 95% CI, 1.21-1.29) to 20 or more pack-years in men (HR = 1.36; 95% CI, 1.3-1.42) compared with 0 pack-years. For women, the researchers found similar results after comparing 5 to 9.9 pack-years (HR = 1.25; 95% CI, 1.04-1.5) and 10 or more pack-years (HR = 1.46; 95% CI, 1.17-1.81) with 0 pack-years.

Additionally, smoking pack-years correlated with an increased risk for NAFLD with intermediate or high fibrosis scores.

For an objective measure compared with self-reporting, the researchers found that urinary cotinine levels correlated with an increased risk for NAFLD. Specifically in men, the hazard ratios were 1.02 (95% CI, 0.92-1.13) for levels between 100 ng/mL and less than 500 ng/mL and 1.13 (95% CI, 1.07-1.21) for levels of 500 ng/mL or higher. In women, the hazard ratios were 1.57 (95% CI, 1.18-2.09) between 100 ng/mL and less than 500 ng/mL and 1.34 (95% CI, 0.98-1.81) for higher levels.

“Our study extends the range of adverse health outcomes positively associated with cigarette smoking,” Jung and colleagues wrote. “The underlying mechanisms of smoking-induced NAFLD and fibrosis are not fully understood yet, but a clearer understanding of smoking-induced NAFLD and fibrosis may help identify patients at high risk of progression.” – by Talitha Bennett

Disclosure: The authors report no relevant financial disclosures.