Buona lettura (mi sento un po' shawn )


JAMA - Journal of the American Medical Association

AN ORIGINAL CONTRIBUTION

Vol. 281 No. 15,
April 21, 1999


--------------------------------------------------------------------------------

A Prospective Study of Egg Consumption and Risk of Cardiovascular Disease in Men and Women


Frank B. Hu, MD; Meir J. Stampfer, MD; Eric B. Rimm, ScD; JoAnn E. Manson, MD; Alberto Ascherio, MD; Graham A. Colditz, MD; Bernard A. Rosner, PhD; Donna Spiegelman, ScD; Frank E. Speizer, MD; Frank M. Sacks, MD; Charles H. Hennekens, MD; Walter C. Willett, MD


Context Reduction in egg consumption has been widely recommended to lower blood cholesterol levels and prevent coronary heart disease (CHD). Epidemiologic studies on egg consumption and risk of CHD are sparse.

Objective To examine the association between egg consumption and risk of CHD and stroke in men and women.

Design and Setting Two prospective cohort studies, the Health Professionals Follow-up Study (1986-1994) and the Nurses' Health Study (1980-1994).

Participants A total of 37,851 men aged 40 to 75 years at study outset and 80,082 women aged 34 to 59 years at study outset, free of cardiovascular disease, diabetes, hypercholesterolemia, or cancer.

Main Outcome Measures Incident nonfatal myocardial infarction, fatal CHD, and stroke corresponding to daily egg consumption as determined by a food-frequency questionnaire.

Results We documented 866 incident cases of CHD and 258 incident cases of stroke in men during 8 years of follow-up and 939 incident cases of CHD and 563 incident cases of stroke in women during 14 years of follow-up. After adjustment for age, smoking, and other potential CHD risk factors, we found no evidence of an overall significant association between egg consumption and risk of CHD or stroke in either men or women. The relative risks (RRs) of CHD across categories of intake were less than 1 per week (1.0), 1 per week (1.06), 2 to 4 per week (1.12), 5 to 6 per week (0.90), and 1 per day (1.08) (P for trend=.75) for men; and less than 1 per week (1.0), 1 per week (0.82), 2 to 4 per week (0.99), 5 to 6 per week (0.95), and 1 per day (0.82) (P for trend=.95) for women. In subgroup analyses, higher egg consumption appeared to be associated with increased risk of CHD only among diabetic subjects (RR of CHD comparing more than 1 egg per day with less than 1 egg per week among diabetic men, 2.02 [95% confidence interval, 1.05-3.87; P for trend=.04], and among diabetic women, 1.49 [0.88-2.52; P for trend=.008]).

Conclusions These findings suggest that consumption of up to 1 egg per day is unlikely to have substantial overall impact on the risk of CHD or stroke among healthy men and women. The apparent increased risk of CHD associated with higher egg consumption among diabetic participants warrants further research.

JAMA. 1999;281:1387-1394




Elevated low-density lipoprotein (LDL) cholesterol is a major risk factor for coronary heart disease (CHD).1 Dietary cholesterol raises LDL cholesterol levels and causes atherosclerosis in numerous animal models.2 In controlled metabolic studies conducted in humans, dietary cholesterol raises levels of total and LDL cholesterol in blood,3, 4 but the effects are relatively small compared with saturated and transfatty acids.5, 6 Studies have found that individuals vary widely in their responses to dietary cholesterol based on monitoring their plasma levels.7, 8 Prospective cohort studies on the relationship of dietary cholesterol with risk of CHD have been inconsistent, with a significant association found in some,9, 10 but not in most studies.11-17

To avoid elevations in blood cholesterol and reduce CHD risk, the public has been advised to consume no more than 300 mg/d of cholesterol and limit consumption of eggs, which contain about 213 mg of cholesterol per egg.1, 18 However, eggs contain many other nutrients besides cholesterol, including unsaturated fats, essential amino acids, folate, and other B vitamins. In addition, consumption of eggs instead of carbohydrate-rich foods may raise high-density lipoprotein (HDL) cholesterol levels19, 20 and decrease blood glycemic and insulinemic responses.21 For these reasons, it is useful to study directly the relationship of egg consumption with risk of CHD, but few epidemiologic studies have addressed this association.22-24 In this article, we examine prospectively the association between egg consumption and risk of CHD and stroke in 2 large cohorts of men and women.




METHODS


The Health Professionals Follow-up Study

The Health Professionals Follow-up Study (HPFS) began in 1986 when 51,529 men who were US health professionals (dentists, optometrists, pharmacists, podiatrists, and veterinarians), aged 40 to 75 years, answered a detailed questionnaire that included a comprehensive diet survey and items on lifestyle practice and medical history. Follow-up questionnaires were sent in 1988, 1990, 1992, and 1994 to update information on potential risk factors and to identify newly diagnosed cases of cardiovascular and other diseases. We excluded from the analysis men who did not satisfy the a priori criteria of reported daily energy intake between 3360 and 17,640 kJ or who left blank more than 70 items of the 131 total food items in the diet questionnaire (n=1152). We also excluded men with prior diagnoses of cardiovascular disease (n=5182) or cancer (n=1644) at baseline. In the primary analyses, we also excluded men who reported diabetes mellitus (n=1187) or hypercholesterolemia (n=4458) at baseline because these diagnoses could have led to changes in diet. Incidence of CHD and stroke during the subsequent 8 years was monitored for 37,851 men during follow-up. The follow-up rate for nonfatal events was 97% of the total potential person-years of follow-up.

The Nurses' Health Study

The Nurses' Health Study (NHS) cohort was established in 1976 when 121,700 women who were registered nurses residing in 11 large states, aged 30 to 55 years, provided detailed information about their medical history and lifestyle characteristics.25 Every 2 years, follow-up questionnaires have been sent to update information on potential risk factors and to identify newly diagnosed cases of CHD, stroke, and other diseases. In 1980, a 61-item food frequency questionnaire was included to assess intake of specific fats and other nutrients. In 1984, the food frequency questionnaire was expanded to include 116 items. Similar questionnaires were used to update diet in 1986 and 1990. The reproducibility and validity of the food frequency questionnaires have been described in detail elsewhere.26, 27

After up to 4 mailings, 98,462 women returned the 1980 diet questionnaire. We excluded those who left 10 or more items blank, those with implausibly high or low scores for total food intake or energy intake (ie, <2100 kJ/d or >14,700 kJ/d) (n=5994), and those with previously diagnosed cancer (n=3526), cardiovascular disease (n=1812), high blood cholesterol (n=1821), or diabetes (n=4122) at baseline. Incidence of CHD and stroke during the subsequent 14 years was monitored for 80,082 women during follow-up. The follow-up rate for nonfatal events was 98% of the total potential person-years of follow-up.

Assessment of Egg Consumption

Validated dietary questionnaires were sent to the HPFS participants in 1986 and 1990 and the NHS participants in 1980, 1984, 1986, and 1990. In all the questionnaires, we asked the participants how often, on average, during the previous year they had consumed eggs (unit of consumption was 1 egg). Nine responses were possible, ranging from never to 6 or more times per day. We divided the participants into 5 categories (<1 per week, 1 per week, 2-4 per week, 5-6 per week, 1 per day) based on the frequency distribution of egg consumption. In a validation study in a subsample of the participants, the correlation coefficent between intakes of eggs assessed by the diet questionnaire and by multiple week diet records was 0.8 for both men28 and women.29 We also computed intake of eggs included in other foods such as cakes, cookies, pancakes, muffins, sweet rolls, and donuts. The amount of eggs estimated from other foods was relatively small in both cohorts (men, 0.4 egg per week; women, 0.3 egg per week), so we used the reported egg consumption as our primary exposure variable. In a secondary analysis, we examined the effect of computed total egg consumption.