National Health And Examination Survey Research Articles

Estimation of attributable number of deaths and standard errors from simple and complex sampled cohorts

Estimates of the attributable number of deaths (AD) from all causes can be obtained by first estimating population attributable risk (AR) adjusted for confounding covariates, and then multiplying the AR by the number of deaths determined from vital mortality statistics that occurred in the population for a specific time period. Proportional hazard regression estimates of adjusted relative hazards obtained from mortality follow-up data from a cohort is combined with a joint distribution of risk factor and confounders to compute an adjusted AR. Two estimators of adjusted AR are examined. These estimators differ according to which reference population is used to obtain the joint distribution of risk factor and confounders. Two types of reference populations were considered: (i) the population represented by the baseline cohort and (ii) a population that is external to the cohort. Methods used in survey sampling are applied to obtain estimates of the variance of the AD estimator. These variances can be applied to data that range from simple random samples to multistage stratified cluster samples, which are used in national household surveys. The variance estimation of AD is illustrated in an analysis of excess deaths due to having a non-ideal body mass index using the second National Health and Examination Survey (NHANES) Mortality Study and the 1999-2002 NHANES. These methods can also be used to estimate the attributable number of cause-specific deaths and their standard errors when the time period for the accrual of deaths is short.

Body Mass Index, Waist Circumference And Physical Activity

Dietary guidance stresses the importance of addressing energy balance to prevent obesity, and minimize chronic disease risk. Energy balance is determined by comparing energy intake to energy expenditure. However, energy balance assessment is often complicated by incomplete or inaccurate food intake or physical activity (PA) information. PURPOSE To use two standard indicators of disease risk, body mass index (BMI) and waist circumference (WC), as a measure of long term weight status; and to combine with PA classification to assess current energy balance status. METHODS Used measured BMI and WC and reported PA data for 4201 adults (2078 men; 2123 women) participating in the National Health and Examination Survey (NHANES), 1999–2000. BMI categories: normal <25; overweight, 25–29.99; obese, 30–34.9; 35–39.9; and > 39.9 and two WC categories: normal or at risk (>102 cm for men and > 88 cm for women) were grouped into five weight risk categories for obesity (normal, increased, high, very high and extremely high). Reported leisure time and work-related PA were used to classify a person into a sedentary, low active, active or very active category. For energy balance assessment, points were assigned in decreasing order to weight status risk (5 to 0) and PA (5 to 0) category for a combined score (10 to 0). Data were weighted. Univariate and means analysis were done using SAS 8.1. RESULTS Men and women classified at normal weight risk had the highest mean scores at 8.0 and 7.8 points, respectively in contrast to men and women classified at extremely high weight risk with the lowest mean scores at 2.3 and 2.2 points, respectively. Men and women with increased weight risk scored 7.3 and 6.8 points and men and women classified at very high weight risk scored 5.9 and 5.4 points, respectively. Thus, while this scoring system penalizes for past dietary behavior (positive energy balance), the inclusion of PA allows for assessment of current calorie expenditure and assumes a corresponding individual adjustment to energy balance as appropriate based on PA classification. That is, a person at increased risk for obesity who is very active may be closer to energy balance than a normal weight risk person who is sedentary. This scoring system identified that more men than women at increased weight risk are closer to energy balance, more women than men at very high risk are further from energy balance, as are both men and women at extremely high risk. CONCLUSION This method provides a reasonable and field expedient way to assess energy balance status that combines measures of past dietary behavior with current physical activity; thereby, minimizing the influence of reporting limitations.

Toxoplasma gondii infection in the United States, 1999-2000.

Infection with Toxoplasma gondii can lead to congenital and acquired disease, resulting in loss of vision and neurologic illness. We tested sera collected in the National Health and Examination Survey (NHANES) from 1999–2000 for T. gondii–specific immunoglobulin G antibodies and compared these results with results from sera obtained in the NHANES III survey (1988–1994). NHANES collects data on a nationally representative sample of the U.S. civilian population. Of 4,234 persons 12–49 years of age in NHANES 1999–2000, 15.8% (age-adjusted, 95% confidence limits [CL] 13.5, 18.1) were antibody positive; among women (n=2,221) 14.9% (age-adjusted, 95% CL 12.5, 17.4) were antibody positive. T. gondii antibody prevalence was higher among non-Hispanic black persons than among non-Hispanic white persons (age-adjusted prevalence 19.2% vs. 12.1%, p=0.003) and increased with age. No statistically significant differences were found between T. gondii antibody prevalence in NHANES 1999–2000, and NHANES III. T. gondii antibody prevalence has remained stable over the past 10 years in the United States.

Age at Natural Menopause and Mortality

PURPOSE: The purpose of this study was to examine the association between age at menopause and mortality in a population-based sample of women in the United States.METHODS: This study was based on data from the National Health and Examination Survey (NHANES) Epidemiologic Follow-up Study; 3191 women aged 50–86 years were included. There were 345 deaths over a mean follow-up time of 4.0 years. We used age-stratified and Poisson regression procedures to assess mortality risk by age at natural menopause, with adjustment for age, duration of follow-up, race, education, smoking, and use of hormone replacement therapy. We conducted a separate analysis for surgical menopause with bilateral oophorectomy.RESULTS: Compared with women who were menstruating to age 50 or later, the adjusted mortality rate ratios (RR) were 1.50 (95% confidence interval (CI), 0.97–2.34) for women with a natural menopause at age < 40, 1.04 (95% CI, 0.72–1.51) for those with menopause at age 40–44, and 0.96 (95% CI, 0.72–1.26) for those with menopause at age 45–49. Women with a natural menopause at age 40–44 years experienced an increased risk of cancer-related mortality (adjusted RR 2.34, 95% CI, 1.20–4.58). No age-related increased mortality risk was seen among women who had surgical menopause with bilateral oophorectomy.CONCLUSIONS: This study provides some support for the concept that age at natural menopause serves as a biological marker of health and aging, with potential implications extending beyond cardiovascular diseases.