Dietary inflammatory index and risk of lung cancer and other respiratory conditions among heavy smokers in the COSMOS screening study

Our plain-English summary of Dietary inflammatory index and risk of lung cancer and other respiratory conditions among heavy smokers in the COSMOS screening study, by P. Maisonneuve, N. Shivappa, J.R. Hébert, et al (European Journal of Nutrition, 2016).

The study

• Authors: P. Maisonneuve, N. Shivappa, J.R. Hébert, M. Bellomi, C. Rampinelli, R. Bertolotti, L. Spaggiari, D. Palli, G. Veronesi, P. Gnagnarella
• Journal: European Journal of Nutrition
• Published: 2016;55(3):1069-79
• Cited by: 65 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: To test whether the inflammatory potential of diet, as measured using the dietary inflammatory index (DII), is associated with risk of lung cancer or other respiratory conditions and to compare results obtained with those based on the aMED score, an established dietary index that measures adherence to the traditional Mediterranean diet.

Methods: In 4336 heavy smokers enrolled in a prospective, non-randomized lung cancer screening program, we measured participants' diets at baseline using a self-administered food frequency questionnaire from which dietary scores were calculated. Cox proportional hazards and logistic regression models were used to assess association between the dietary indices and lung cancer diagnosed during annual screening, and other respiratory outcomes that were recorded at baseline, respectively.

Results: In multivariable analysis, adjusted for baseline lung cancer risk (estimated from age, sex, smoking history, and asbestos exposure) and total energy, both DII and aMED scores were associated with dyspnoea (p trend = 0.046 and 0.02, respectively) and radiological evidence of emphysema (p trend = 0.0002 and 0.02). After mutual adjustment of the two dietary scores, only the association between DII and radiological evidence of emphysema (Q4 vs. Q1, OR 1.30, 95 % CI 1.01-1.67, p trend = 0.012) remained statistically significant. At univariate analysis, both DII and aMED were associated with lung cancer risk, but in fully adjusted multivariate analysis, only the association with aMED remained statistically significant (p trend = 0.04).

Conclusions: Among heavy smokers, a pro-inflammatory diet, as indicated by increasing DII score, is associated with dyspnoea and radiological evidence of emphysema. A traditional Mediterranean diet, which is associated with a lower DII, may lower lung cancer risk.

In plain English

This Italian study followed 4336 heavy smokers in the COSMOS lung cancer screening program, enrolled 2004–2005. Their food questionnaires were scored with a dietary inflammatory index (DII; higher is more pro-inflammatory) and a Mediterranean diet score (aMED, 0–9). Analyses adjusted for baseline risk based on age, sex, smoking and self-reported asbestos exposure, but gave no separate results for asbestos exposure. A past history of asbestosis was reported by 3, 1, 3 and 2 participants across the DII quarters, with no trend. Over a median 8.5 years, 200 lung cancers were diagnosed. Unadjusted, the highest DII quarter had more lung cancer than the lowest (1.64, 95% CI 1.10–2.44). This was not significant after adjustment. Those scoring 8–9 on aMED, versus 0–1, had lower lung cancer risk (HR 0.20, 95% CI 0.04–0.90), with 2 cancers in that group. Adjusted for baseline risk and energy, the top DII quarter more often reported breathlessness (OR 1.30, 95% CI 1.03–1.64) and had emphysema on baseline CT (OR 1.41, 95% CI 1.13–1.75). With aMED also adjusted for, only the CT emphysema link stayed statistically significant (OR 1.30, 95% CI 1.01–1.67). The authors noted single diet measurement and few lung cancers as limitations.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective cohort analysis within a non-randomized lung cancer screening trial. Lung cancer was followed over time. Other respiratory conditions were recorded once, at the baseline visit.
• Who was studied: 4336 of 5203 COSMOS participants who returned a completed food frequency questionnaire. All were asymptomatic volunteers in Italy, enrolled 2004–2005, aged 50 or older, who were current smokers or had quit less than 10 years earlier and had smoked at least 20 pack-years. 66.1% were men, 79.8% were current smokers, and the median age was 57.
• Exposure: Diet over the previous year, from a 188-item food frequency questionnaire. It was scored as the dietary inflammatory index (DII, from 24 food parameters) and the alternate Mediterranean diet (aMED) score, ranging 0–9. Asbestos exposure was a single yes/no item, self-reported on the baseline questionnaire. It was used only inside the lung cancer risk score for adjustment and was not studied as an exposure in its own right.
• Main results:
  • Over a median follow-up of 8.5 years (30,960 person-years), lung cancer was diagnosed in 200 participants: 143 men and 57 women.
  • Before adjustment, participants in the highest DII quarter had a higher lung cancer risk than those in the lowest quarter: 1.64 (95% CI 1.10–2.44), p trend 0.02. The text calls this an OR, while the figure table calls it an HR. After adjustment the association was no longer statistically significant. Adjusted for risk and energy it was HR 1.54 (0.93–2.55). With aMED also adjusted for, it was HR 1.16 (0.65–2.07), p trend 0.76.
  • Participants with aMED scores of 8–9 (158 people, 2 lung cancers) had a lower lung cancer risk than those scoring 0–1. This held with adjustment that included the DII score. The text gives HR 0.20 (95% CI 0.04–0.90); the figure table gives 0.20 (0.04–0.91), p trend 0.04.
  • After adjustment for baseline lung cancer risk and energy intake, participants in the highest DII quarter were more likely than the lowest to report dyspnoea (OR 1.30, 95% CI 1.03–1.64, p trend 0.046). They were also more likely to have emphysema on the baseline CT scan (OR 1.41, 95% CI 1.13–1.75, p trend 0.0002). Both conditions were recorded at baseline.
  • When the two diet scores were adjusted for each other, only the link between DII and emphysema on CT remained statistically significant (highest vs lowest quarter OR 1.30, 95% CI 1.01–1.67). The dyspnoea association did not (OR 1.23, 0.94–1.61, p trend 0.20).
  • After adjustment for risk and energy, the aMED score was associated with dyspnoea (p trend 0.02) and with emphysema on CT (p trend 0.02). Neither association was statistically significant after further adjustment for DII (p trend 0.12 and 0.73).
  • A past history of asbestosis was reported by 3, 1, 3 and 2 participants in the four DII quarters, lowest to highest. There was no trend with DII (p trend 0.88).
• The authors' conclusion: The authors concluded that among heavy smokers, a pro-inflammatory diet (higher DII) is associated with dyspnoea and with emphysema seen on CT. They also concluded that a traditional Mediterranean diet, which goes with a lower DII, may lower lung cancer risk.
• Limitations the authors state:
  • Diet was measured with one questionnaire at the start, and participants may have changed their diets during the study.
  • Food frequency questionnaires are subject to measurement error.
  • Recall bias is possible for conditions reported at the baseline interview, such as pneumonitis, COPD or dyspnoea.
  • There were relatively few lung cancers, which limited statistical power.
  • Many outcomes were tested, so some positive associations may be due to chance.
  • The two diet scores were highly correlated, so adjusting for both may have over-adjusted the models.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Low-Dose CT Screening, Asbestos Exposure, Emphysema, Multivariate Analysis.

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