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There is a rumour which states that chefs increase their likelihood of developing lung cancer if they work for long periods of time in the kitchen with oily steam.

Does anybody here have such evidence?

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    Possible claim source: news.discovery.com/human/fatty-foods-cooking-health.htm – Sean Duggan May 16 '16 at 13:17
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    I heard (but cannot now find) that workers in popcorn packaging factories have to wear masks, to prevent inhaling the fumes of the "buttery flavor" oil that is used. – GEdgar May 16 '16 at 15:28
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    @GEdgar That'd presumably be due to diacetyl, a chemical used to give it the buttery flavor. Also presumably not involved here. – derobert May 16 '16 at 16:10
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    Don't workers in most food packaging and processing have to wear masks to protect the food as well? – Roger May 17 '16 at 19:46
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    This needs to show there is a notable claim. Link to a source. – matt_black May 18 '16 at 8:49
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There have been a number of case-control studies on Chinese women. Here are three open-access papers:

  • Ko et al. (2000). "Chinese Food Cooking and Lung Cancer in Women Nonsmokers". Amer. J. Epidemiology 151(2) pp. 140–147.

    The subjects were 131 nonsmoking incident cases with newly diagnosed and histologically confirmed primary carcinoma of the lung, 252 hospital controls hospitalized for causes unrelated to diseases of smoking, and 262 community controls; all controls were women nonsmokers matched by age and date of interview. Details on cooking conditions and habits were collected, in addition to other epidemiologic data. Lung cancer risk increased with the number of meals per day to about threefold for women who cooked these meals each day. The risk was also greater if women usually waited until fumes were emitted from the cooking oil before they began cooking (adjusted odds ratios = 2.0–2.6) and if they did not use a fume extractor (adjusted odds ratios = 3.2–12.2).

    This study was carried out in Kaohsiung, Taiwan.

  • Metayer et al. (2002). "Cooking oil fumes and risk of lung cancer in women in rural Gansu, China". Lung Cancer 35 pp. 111–117.

    We investigated the association between lung cancer and locally made rapeseed and linseed oils in a population-based case-control study in Gansu Province, China. Two hundred and thirty-three incident, female lung cancer cases diagnosed from 1994–98 were identified. A control group of 459 women was selected from census lists and were frequency matched on age and prefecture. Interviewers obtained information on cooking practices and cooking oil use. The odds ratio (OR) for lung cancer associated with ever-use of rapeseed oil, alone or in combination with linseed oil, was 1.67 (95% CI 1.0–2.5).

  • Yu et al. (2006). "Dose-Response Relationship between Cooking Fumes Exposures and Lung Cancer among Chinese Nonsmoking Women". Cancer Res. 66; p. 4961.

    We carried out a population-based case-control study in Hong Kong. Cases were Chinese female nonsmokers with newly diagnosed primary lung cancer. Controls were female nonsmokers randomly sampled from the community, frequency matched by age groups. Face-to-face interviews were conducted using a standardized questionnaire. The “total cooking dish-years,” categorized by increments of 50, was used as a surrogate of cooking fumes exposure. Multiple unconditional logistic regression was used to estimate the odds ratios (OR) for different levels of exposure after adjusting for various potential confounding factors. We interviewed 200 cases and 285 controls. The ORs of lung cancer across increasing levels of cooking dish-years were 1, 1.17, 1.92, 2.26, and 6.15. After adjusting for age and other potential confounding factors, the increasing trend of ORs with increasing exposure categories became clearer, being 1, 1.31, 4.12, 4.68, and 34.

Case-control studies are not the highest level of medical evidence, but I couldn't find a longitudinal or cohort study on this question.

Statistical discussion. An odds ratio is a statistic computed by dividing the odds of exhibiting the condition of interest (here, cooking with oil) for study members with the outcome (here, lung cancer) by the odds for study members without the outcome. For example in Metayer et al. (2001), of the 233 cases 148 cooked with rapeseed oil and 85 did not, while of 459 controls 205 did so and 254 did not. This gives a raw odds ratio of (148 ÷ 85) ÷ (205 ÷ 254) = 2.16. The authors adjusted this computation to take account of socioeconomic differences between the make-up of the case and control groups, getting the adjusted odds ratio 1.67 reported in the abstract.

Odds ratios are straightforward to compute but hard to interpret. One would much rather know the risk ratio: in this case, how much more likely is someone in the population to contract lung cancer if they cook with oil. However, for rare enough conditions, the odds ratio is often a good estimate for the risk ratio (the rare disease assumption). The incidence of lung cancer in women in China is rare (about 30 per 100,000 per year) so we could summarize Metayer et al. as saying that they found that there was a 67% higher risk of contracting lung cancer among women who cooked with rapeseed oil. But we should also note that the 95% confidence interval (1.0-2.5) is quite wide and includes 1.0 (meaning that the study is compatible with there being no increase in risk).

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    I agree with Zack. An answer is expected to contain citations to data but not exclusively citations. Not everybody interested in a skeptical answer is able to easily extrapolate an answer from "raw articles", and that's one reason why this site is useful... – Bakuriu May 16 '16 at 16:18
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    @Bakuriu: The site rules discourage original research: "It is acceptable to provide a collection of evidence, but not to apply non-trivial calculations that require a community of experts to evaluate." I did look for a systematic review but did not find one that was open access. – Gareth Rees May 16 '16 at 16:53
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    I think this is an ideal answer for this question: it cites on-point peer-reviewed primary sources, and provides enough context to understand what the epidemiology says and what it doesn't. – Crashworks May 17 '16 at 20:12
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I haven't found a study that specifically mentions chefs, but here is a study about Chinese women and lung cancer:

Fumes from meat cooking and lung cancer risk in Chinese women

Chinese women are recognized to have a high incidence of lung cancer despite a low smoking prevalence. Several studies have implicated domestic exposure to cooking fumes as a possible risk factor, although the exact carcinogens have yet to be identified. Heterocyclic amines are known carcinogens, which have been identified in cooked meat, and also in fumes generated during frying or grilling of meats. We conducted a case-control study of 303 Chinese women with pathologically confirmed, primary carcinomas of the lung and 765 controls to examine the association between exposure to meat cooking and lung cancer risk. Data on demographic background, smoking status, and domestic cooking exposure, including stir-frying of meat, were obtained by in-person interview while in hospital. The response rates among eligible cases and controls were 95.0 and 96.9%, respectively. The proportion of smokers (current or ex-smokers) among cases and controls was 41.7 and 13.1%, respectively. Adenocarcinomas comprised 31.5% of cancers among smokers and 71.6% among nonsmokers. When cases were compared with controls, the odds ratio (OR) for lung cancer (all subtypes) among ex-smokers was 4.3 [95% confidence interval (CI) 2.7-6.8] and that among current smokers was 5.0 (95% CI, 3.4-7.3). Among smokers, women who reported that they stir-fried daily in the past had a significantly increased risk of lung cancer (adjusted OR, 2.0; 95% CI, 1.0-3.8) and among these women, risk was enhanced for those who stir-fried meat daily (OR, 2.7; 95% CI, 1.3-5.5). Women who stir-fried daily but cooked meat less often than daily did not show an elevated risk (OR, 1.0. 95% CI, 0.5-2.4). Risk was further increased among women stir-frying meat daily who reported that their kitchen was filled with oily fumes during cooking (OR, 3.7; 95% CI, 1.8-7.5). These cooking practices on their own did not increase risk among nonsmokers in our study population. Our results suggest that inhalation of carcinogens, such as heterocyclic amines generated during frying of meat, may increase the risk of lung cancer among smokers. Further studies in different settings are warranted to examine this possibility, which may also help to explain the higher risk observed among women smokers compared with men.

However, it should be noted that the results did not show the oily fumes themselves causing cancer, but rather that it seems to increase the risk if the person inhaling the fumes is also a smoker.

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Two further points

Smoke from burning solid fuel is known to cause lung cancer, so many studies in the developing world are looking at smoke exposure from fires (1).

There is a little bit of toxicology data (2) for mineral oils suggesting that occupational exposure to pure oils might not be harmful, but it is also well known that heated oils can contain very different chemicals from pure oils.

So, I don't really know, but these will get you started on looking for an answer.

(1) http://publications.iarc.fr/Book-And-Report-Series/Iarc-Monographs-On-The-Evaluation-Of-Carcinogenic-Risks-To-Humans/Household-Use-Of-Solid-Fuels-And-High-Temperature-Frying-2010

(2) Respiratory Toxicology of Mineral Oils in Laboratory Animals Walden E. Dalbey , Robert W. Biles Applied Occupational and Environmental Hygiene Vol. 18, Iss. 11, 2003

  • This would be a better answer if it quoted some of the key conclusions from the links in the answer. – matt_black May 18 '16 at 8:53

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