Prospective Study of Cured Meats Consumption and Risk of Chronic Obstructive Pulmonary Disease in Men

Raphaëlle Varraso; Rui Jiang; R. Graham Barr; Walter C. Willett; Carlos A. Camargo, Jr.

Disclosures

Am J Epidemiol. 2007;166(12):1438-1445. 

In This Article

Materials and Methods

Study Population

The Health Professionals Follow-up Study, a prospective cohort study, began in 1986 when 51,529 US health professionals (dentists, optometrists, pharmacists, podiatrists, and veterinarians) aged 40-75 years answered a detailed mailed questionnaire that included a diet survey and items on lifestyle practice and medical history. Follow-up questionnaires were sent every 2 years thereafter to update information on smoking habits, physical activity, weight, and other risk factors and to ascertain newly diagnosed medical conditions. Dietary intake data were collected in 1986 and every 4 years thereafter with a 131-item food frequency questionnaire. The study is being conducted according to the ethical guidelines of Brigham and Women's Hospital (Boston, Massachusetts).

Men who did not satisfy a reported daily energy intake between 3.3 and 17.6 MJ (800 and 4,200 kcal) or who left blank more than 70 of a total of 131 food items on the diet questionnaire were excluded. We further excluded 232 men with confirmed COPD at baseline or missing date of diagnoses, 1,834 with reported asthma, and 272 with unconfirmed COPD at baseline or during the follow-up. The final baseline population included 42,915 men.

Consumption of Cured Meats

Cured meats consumption was defined as the total consumption of processed meats, bacon, and hot dogs, which was asked as three separate questions: "How often on average have you used the amount specified during the past year: 1) processed meats, e.g., sausage, salami, bologna, ... (slice); 2) bacon (two slices); 3) hot dogs?".[1] Participants indicated their average frequency of consumption over the past year in terms of the specified serving size by checking one of nine frequency categories ranging from "almost never" to "≥6 times/day." The selected frequency category for each food item was converted to a daily intake. Cured meats consumption was identified from food frequency questionnaires administrated in 1986, 1990, and 1994. To reduce measurement errors and to represent long-term dietary intake, we calculated the cumulative average of cured meats consumption, which was then divided into five categories according to the number of servings per week: never/almost never, <1 serving/week, 1-3 servings/week, 4-6 servings/week, and at least once/day. The cumulative average incorporated repeated measures of diet.[14] With this approach, the 1986 cured meats consumption was used to predict newly diagnosed COPD in 1986-1990; an average of the 1986 and 1990 cured meats consumption was used to predict COPD in 1991-1994; and the average of the 1986, 1990, and 1994 cured meats consumption was used to predict COPD from 1995 to 1998. The individual associations with processed meats, bacon, and hot dogs were also investigated in relation to newly diagnosed COPD. The cumulative average was calculated for each one of these cured meats and then divided into three categories according to the number of servings per week (never/almost never, <1 serving/week, and at least once/week).

Assessment of Respiratory Phenotypes

Because the Health Professionals Follow-up Study includes many participants dispersed throughout the United States and is conducted by mail, the diagnosis of COPD was assessed by questionnaire and did not include spirometry. Supplemental questionnaires were sent in 1998 and 2000 to all participants who reported chronic bronchitis or emphysema on the biennial questionnaires. Self-reported COPD was defined by the affirmative response to physician-diagnosed chronic bronchitis or emphysema on the biennial questionnaires and by confirmation of chronic bronchitis, emphysema, or COPD on the supplemental COPD questionnaire, plus report of a diagnostic test at diagnosis (pulmonary function testing, chest radiograph, or chest computed tomography). This epidemiologic definition was validated in a random sample of another cohort of health professionals.[15] Between 1986 and 1998, 111 cases of newly diagnosed COPD that were reported met these criteria.

Asthma was also self-reported and was defined by a new physician diagnosis of asthma on the biennial questionnaires and by confirmation on the supplemental asthma questionnaire, plus use of medication for asthma in the 12 months preceding the supplemental questionnaire. Between 1986 and 1998, 212 new cases of adult-onset asthma were reported.

Assessment of Other Variables

Total calorie intake was estimated through the food frequency questionnaire, expressed in kilocalories per day. Information on smoking status included the categories never smokers, former smokers, and current smokers. We further characterized smokers using their lifetime pack-years of smoking and pack-years squared; prior analyses have demonstrated that including both measures optimally controls for the association between smoking and COPD risk. Data on race/ethnicity and region also were collected. Race/ethnicity was categorized in two classes (White, non-White), and US region was categorized in three classes (East, South, Central; Mountain; and other regions). Body mass index, physical activity, and multivitamin use were assessed every 2 years by self-reported questionnaires. Body mass index was calculated as weight (kg)/height (m)2 and was categorized into four classes: <20.0, 20.0–24.9, 25.0–29.9, and ≥30.0 kg/m2. Men also reported physical activity, including a variety of activities such as walking, bicycle riding, swimming, or tennis. Physical activity was measured in metabolic equivalent hours per week, where 1 metabolic equivalent was equal to the energy expended at the basal metabolic rate or at rest.

Previously, in this cohort of men, a strong association between dietary patterns and the risk of newly diagnosed COPD was reported.[16] The "prudent pattern" was loaded by a high consumption of fruits, vegetables, fish, and whole grains and was negatively associated with newly diagnosed COPD, whereas the "Western pattern" was loaded by a high intake of refined grains, cured and red meats, desserts and sweets, and French fries and was positively associated with newly diagnosed COPD. Because cured meats are a food group included in the Western pattern, we derived a new Western pattern without contribution from cured meats, and we termed this the "modified Western pattern."

Statistical Analysis

Statistical analyses included chi-squared, analysis of variance, linear regression, and Cox proportional hazards regression models. Cox proportional hazards models were adjusted for age and energy intake and then for seven variables (smoking status, pack-years, pack-years squared, race/ethnicity, US region, body mass index, and physical activity). We intensively adjusted for smoking (smoking status, pack-years, pack-years squared), because it is the main risk factor for COPD and because smokers tend to have a different diet than do nonsmokers.[17] We also adjusted for race/ethnicity, because death rates from COPD are rising faster in African Americans than in Whites[18] and because diet is highly related to racial/ethnic identity. To take into account geographic disparities in COPD and diet across the United States, we also adjusted for US region. The adjustment for body mass index and physical activity was motivated by the strong interrelations among diet, body mass index, and physical activity. Furthermore, low body mass index is highly related to COPD,[19] and it has been reported that physical activity is associated with lower risk of COPD.[20]

In a subsequent analysis, we also adjusted for the prudent dietary pattern and the "modified Western pattern" to better assess the individual effect of cured meat intake and to control for the other potential deleterious effects of the Western diet. All analyses were conducted using SAS, version 9, software (SAS Institute, Inc., Cary, North Carolina).

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