Mortality by cause of death and risk behaviors in farmers versus non-farmers: the importance of avoiding the healthy worker effect

Our plain-English summary of Mortality by cause of death and risk behaviors in farmers versus non-farmers: the importance of avoiding the healthy worker effect, by G. Zhao, E. Ronda, L. Cea, et al (International Archives of Occupational and Environmental Health, 2019).

The study

• Authors: G. Zhao, E. Ronda, L. Cea, J. Pulido, G. Barrio, E. Regidor
• Journal: International Archives of Occupational and Environmental Health
• Published: 2019;92(4):599-608
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To compare mortality by cancer sites and by other specific causes of death, and the prevalence of risk behaviors in farmers and non-farmers in Spain.

Methods: Mortality by cause of death was calculated based on a longitudinal study with 10-years follow-up of 9.5 million men and 6 million women aged 20-64 years who were employed in 2001. The prevalence of risk behaviors was calculated from the 2001 National Health Survey in the 6464 employed men and 5573 employed women aged 20-64. The study subjects were grouped as farmers and non-farmers. For each cause of death, we estimated the ratio of age-standardized mortality rates, and for each risk behavior we estimated the age-standardized prevalence ratio in farmers versus non-farmers.

Results: In men, the mortality rate for most cancer sites did not differ significantly between farmers and non-farmers, except for cancers of the lip, oral cavity, stomach, larynx and skin epidermoid carcinoma-which was higher in farmers-and cancers of the liver, pancreas and mesothelioma-which was lower in farmers. In contrast, farmers had a higher rate of mortality from most other diseases and from external causes of death. In women, farmers showed lower mortality from lung cancer, breast cancer and chronic lower respiratory disease, and higher mortality from external causes. The prevalence of smoking, excessive alcohol consumption, physical inactivity and obesity was higher in farmers than in non-farmers, except smoking and excessive alcohol consumption in women where prevalence was lower in farmers.

Conclusions: Findings are different from those found in other studies. In men, greater exposure to the sun and the higher prevalence of risk behaviors in farmers could explain their excess mortality from some cancer sites and the other causes of death. However, other factors may be behind this excess risk of mortality from these causes, given that farmers did not show higher mortality from some cancers related to smoking. In women, no differences were observed in mortality rate for majority of causes of death between farmers and non-farmers.

In plain English

This study compared causes of death in Spanish farmers with all other employed people. The authors followed 9,579,759 men and 5,919,413 women aged 20 to 64 who were working at the 2001 census. Follow-up ran to the end of 2011 through linked registries. They also used the 2001 National Health Survey to compare smoking, excessive alcohol consumption, physical inactivity, obesity and insufficient fruit or vegetable consumption. Farming was identified only by job title. No workplace exposures were measured; asbestos is not mentioned. Compared with other workers of the same sex, the age-standardized all-cause mortality rate ratio was 1.10 (95% CI 1.08–1.11) for male farmers and 1.00 (95% CI 0.96–1.05) for female farmers. Male farmers had a lower mesothelioma death rate than non-farmer men: 26 deaths, rate ratio 0.65 (95% CI 0.44–0.96). Among women, 3 mesothelioma deaths in farmers gave a ratio of 0.73 (0.23–2.33), which was not statistically significant. Male farmers had higher death rates from cancers of the lip, oral cavity, stomach and larynx, skin epidermoid carcinoma, suicide and transport accidents. The authors suggested sun exposure and risk behaviors could be behind some excesses.

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: National census-linked cohort study with about 10 years of follow-up (2001–2011), combined with a cross-sectional analysis of the 2001 National Health Survey
• Who was studied: 9,579,759 men and 5,919,413 women in Spain aged 20 to 64 who were employed at the November 2001 census (454,961 male and 165,350 female farmers). Risk behaviors came from 6464 employed men and 5573 employed women in the 2001 National Health Survey.
• Exposure: Occupation as a farmer (skilled self-employed, skilled salaried workers and laborers in agriculture) versus all other occupations, recorded at the 2001 census. No specific exposures, including asbestos, were measured.
• Main results:
  • The age-standardized all-cause mortality rate ratio for farmers versus non-farmers was 1.10 (95% CI 1.08–1.11) in men and 1.00 (95% CI 0.96–1.05) in women.
  • In men, mesothelioma mortality was lower in farmers than in non-farmers: 26 deaths in farmers (rate 0.6 per 100,000 person-years) versus 610 in non-farmers (rate 0.9), rate ratio 0.65 (95% CI 0.44–0.96).
  • In women, mesothelioma deaths numbered 3 in farmers and 93 in non-farmers, rate ratio 0.73 (95% CI 0.23–2.33). This was not a significant difference.
  • In men, farmers had higher mortality from cancers of the lip (2.67, 1.25–5.73), oral cavity (1.25, 1.10–1.42), stomach (1.13, 1.03–1.23), larynx (1.21, 1.06–1.38) and skin epidermoid carcinoma (1.55, 1.01–2.40). Lung cancer mortality did not differ between male farmers and non-farmers.
  • In men, the highest rate ratios for farmers were for suicide 1.80 (1.67–1.94), exposure to inanimate mechanical forces 1.63 (1.29–2.06) and transport accidents 1.58 (1.48–1.69).
  • In women, farmers had lower mortality from lung cancer (0.56, 0.46–0.67) and breast cancer (0.80, 0.70–0.91), and higher mortality from thyroid cancer (1.95, 1.01–3.78).
  • Among employed men in the health survey, farmers had higher prevalence of smoking (prevalence ratio 1.09, 1.01–1.19), excessive alcohol consumption (1.66, 1.35–2.04), physical inactivity (1.37, 1.26–1.48) and obesity (1.44, 1.17–1.77). Insufficient fruit or vegetable consumption did not differ (0.99, 0.93–1.06).
• The authors' conclusion: The authors concluded that male farmers in Spain had higher mortality than other employed men from some cancer sites and from several other causes. They suggested that greater sun exposure and higher prevalence of risk behaviors could be behind this, though other factors may also play a role. In women, most causes of death did not differ between farmers and non-farmers.
• Limitations the authors state:
  • The study did not include measures of workplace exposures or of individual health risk behaviors.
  • The healthy worker effect may not have been completely eliminated.
  • Employment and farmer status were based only on the week before the census, with no information on farm worker or owner status or on time in the job.
  • Occupation in agriculture is probably not a good indicator of exposure to specific pesticides.

Topics

Medical terms in this study, explained in our Lexicon: Healthy Worker Effect, Carcinoma, Mesothelioma, Lung Cancer.

Related studies

• Mortality among North Carolina construction workers, 1988-1994 — E. Wang, J.M. Dement, et al. (1999)
• Cohort mortality study of rock salt workers in Italy — M. Tarchi, D. Orsi, et al. (1994)
• Causes of death in a cohort of 260 plutonium workers — B. Gold, R.L. Kathren (1998)
• Mortality and cancer morbidity in a cohort of Canadian petroleum workers — R.J. Lewis, A.R. Schnatter, et al. (2003)
• A historical cohort mortality study of workers exposed to asbestos in a refitting shipyard — N. Kurumatani, Y. Natori, et al. (1999)
• An updated historical cohort mortality study of workers exposed to asbestos in a refitting shipyard, 1947-2007 — K. Tomioka, Y. Natori, et al. (2011)

Browse more research in International Archives of Occupational and Environmental Health, or return to medical research.