Are nuts the answer to avoiding lung cancer?

Eating more nuts may help prevent small-cell lung cancer (SCLC) in men, according to a recent study published in Lung Cancer. The benefit was most pronounced in men who were former heavy smokers. Nuts were not protective, however, for other subtypes of cancer, total lung cancer, or in women. Finally, researchers found that consumption of peanut butter offered no protective benefits at all.

“Nuts have recently been hypothesized to conduct cancer-chemopreventive activities because of their antioxidant and anti-inflammatory effects. Several studies have demonstrated inverse associations of nut intake with cancer-related mortality. Nevertheless, evidence regarding the relation between nut consumption and lung cancer risk is limited to three cohort and three case-control studies, and is inconclusive,” wrote Lisette Nieuwenhuis, PhD student, and Piet A. van den Brandt, MD, full professor, Department of Epidemiology, Maastricht University Medical Center+, Maastricht, the Netherlands.

Nieuwenhuis and Dr. van den Brandt had previously collaborated on another study in which they observed an inverse association between the Mediterranean diet and lung cancer risk. They noted that consumption of nuts may have contributed to this effect, particularly in men.

In the current study, Nieuwenhuis and Dr. van den Brandt assessed the possible associations of total nut, tree nut, peanut, and peanut butter consumption with the risk of lung cancer in both men and women enrolled in the prospective, population-based Netherlands Cohort Study (NLCS). They also sought to differentiate the effects based on the four major histologic subtypes of lung cancer: adenocarcinoma, squamous cell carcinoma, SCLC, and large-cell carcinoma. Finally, they studied the effects in those who had never smoked, former smokers, and current smokers.

In 1986, the dietary and lifestyle habits of 120,852 participants (aged 55-69 years) from the NLCS were measured via an 11-page questionnaire designed to assess dietary and cancer risk factors. After 20.3 years of follow-up, Nieuwenhuis and Dr. van den Brandt included 3,720 subjects from a random subcohort of 5,000 and 2,861 subjects with lung cancer for their multivariable, case-cohort analysis.

The most common lung cancer in men was squamous cell carcinoma (38.7%), followed by adenocarcinoma (22.2%). In women, adenocarcinoma was most common (33.5%), followed by squamous cell carcinoma (23.2%).

Among men with lung cancer, mean total nut intake was 7.1 g/d, which was lower than in the subcohort in general, at 7.9 g/d. In women with lung cancer, this mean was 4.9 g/d, which was higher than in the subcohort (4.4 g/d).

Nieuwenhuis and Dr. van den Brandt found that total nut intake was not significantly associated with total lung cancer risk in men or women (P-trend: 0.184 in men and 0.720 in women). Neither was peanut butter intake. In men, they found inverse associations with lung cancer risk that were non-significant.

When they analyzed results according to lung cancer subtype, nut intake had no effects in women. In men with SCLC, they found a significant inverse association between total nut intake of ≥ 10 g/d vs non-nut eaters (HR: 0.62; 95% CI: 0.43-0.89; P-trend: 0.024) after controlling for smoking habits. Again, in men, they found non-significant inverse trends with total nut intake and adenocarcinoma, squamous cell, and large-cell carcinomas. There was a borderline significant association with large-cell carcinoma (HR per 5 g/d increment: 0.95; 95% CI: 0.90-1.00) in men only.

Upon continuous analysis for SCLC in men, they observed an inverse association for tree nut and peanut intake (HR of 0.070 per 5 g/d increment [95% CI: 0.53-0.93], and 0.93 [95% CI: 0.88-0.98, respectively].

When researchers stratified their analyses by smoking status, they found a non-significant inverse association in men who were never-smokers (P-trend: 0.854), a significant inverse association in former smokers (P-trend: 0.007), and no association in current smokers (P-trend: 0.843).

Association by smoking status became significant in men when researchers combined the two highest nut intake categories into one (5+ g/d; P-interaction: 0.042). In men who were former or current smokers, researchers found a borderline significant inverse association between total nut intake and SCLC, and in men who were former heavy smokers, they noted a significant inverse association (P-interaction: 0.075).

In women, there were no clear associations between total nut intake and total lung cancer in never-smokers (P-trend: 0.452), a non-significant inverse association in former smokers (P-trend: 0.549), and a non-significant positive association in current smokers (P-trend: 0.937).

Inverse associations with SCLC in former heavy, current lighter, and current heavy smokers were stronger for tree nut than total nut intake.

“Based on the overall body of evidence from the few prospective cohort studies investigating the relation between nut consumption and lung cancer risk, nut intake might be associated with a reduced risk of lung cancer, in particular the small-cell carcinoma subtype. Cigarette smoking possibly modifies this relation,” concluded Nieuwenhuis and Dr. van den Brandt.

This study was supported by the Dutch CancerSociety.