Thyroid function changes related to use of iodinated water in the U.S. Space Program.

BACKGROUND: The National Aeronautics and Space Administration (NASA) has used iodination as a method of microbial disinfection of potable water systems in U.S. spacecraft and long-duration habitability modules. A review of thyroid function tests of NASA astronauts who had consumed iodinated water during spaceflight was conducted. METHODS: Thyroid function tests of all past and present astronauts were reviewed. Medical records of astronauts with a diagnosis of thyroid disease were reviewed. Iodine consumption by space crews from water and food was determined. Serum thyroid-stimulating hormone (TSH) and urinary iodine excretion from space crews were measured following modification of the Space Shuttle potable water system to remove most of the iodine. RESULTS: Mean TSH significantly increased in 134 astronauts who had consumed iodinated water during spaceflight. Serum TSH, and urine iodine levels of Space Shuttle crewmembers who flew following modification of the potable water supply system to remove iodine did not show a statistically significant change. There was no evidence supporting association between clinical thyroid disease and the number of spaceflights, amount of iodine consumed, or duration of iodine exposure. CONCLUSIONS: It is suggested that pharmacological doses of iodine consumed by astronauts transiently decrease thyroid function, as reflected by elevated serum TSH values. Although adverse effects of excess iodine consumption in susceptible individuals are well documented, exposure to high doses of iodine during spaceflight did not result in a statistically significant increase in long-term thyroid disease in the astronaut population.

Design and current status of the longitudinal study of astronaut health.

BACKGROUND: Information has been collected regarding the immediate physiological effects of spaceflight on humans. However, little is yet known regarding long-term effects. The purpose of this paper is to describe the Longitudinal Study of Astronaut Health (LSAH) and report current mortality data. METHODS: All astronauts selected for the United States Space Program are followed from selection throughout their lifetime or until the end of the study. Comparisons are ground-based Johnson Space Center (JSC) employees matched to the astronauts at a 3:1 ratio by sex-specific age and body mass index. They are followed in the same manner as astronauts. Morbidity and mortality data are obtained from medical records supplemented with study questionnaires. Checks for death certificates are made to ascertain death of participants who miss routine examinations. RESULTS: Current cause-specific mortality rates for astronauts selected from 1959 through 1991 are not statistically different from rates for comparison participants for cardiovascular (p = 0.8112), cancer (p = 0.2382), or other disease (p = 0.5040) mortality. Astronauts have a significantly higher mortality rate due to accidents and injuries (p < 0.0001). CONCLUSIONS: Astronauts have a similar risk of death due to chronic diseases as ground-based participants, but are at greater risk for occupational-related accidental death.

Risk of cancer mortality among the Longitudinal Study of Astronaut Health (LSAH) participants.

BACKGROUND: The potential for occupational radiation exposures in the U.S. Space Program makes cancer risk a major health concern. METHODS: The NASA Medical Operations Branch and KRUG Life Sciences Epidemiology Section at the Johnson Space Center (JSC) investigated the rate of cancer mortality among the astronauts and the comparison participants of the Longitudinal Study of Astronaut Health (LSAH). Medical records are maintained by the JSC Flight Medicine Clinic, JSC Occupational Medicine Clinic, and LSAH. Cause of death data from death certificates were reviewed for cancer mortality. These data were compared with cancer mortality data for the general population residing in the Texas Gulf Coast area. RESULTS: The astronauts had a higher age-specific risk of cancer mortality than the comparison group (SMR = 345; 95% CI = 69.5-756.2), but the difference did not reach statistical significance. Both the astronauts and the comparison group had lower age-specific rates than the general population (SMR = 47, 95% CI = 9.6-105.1; SMR = 17, 95% CI = 3.5-37.9, respectively).

Sex and ethnic differences in use of myocardial revascularization procedures in Mexican Americans and non-Hispanic whites: the Corpus Christi Heart Project.

Age-adjusted rates of percutaneous transluminal coronary angioplasty (PTCA) and aortocoronary bypass surgery (ACBS) were determined for Mexican American (MA) and non-Hispanic white (NHW) patients hospitalized for coronary heart disease. Hypotheses of equal receipt of procedures between gender and ethnic groups were tested. Following myocardial infarction (MI), women were less likely than men to receive either procedure (22 versus 32%, p < 0.01), and MA were less likely than NHW to receive PTCA (13 versus 23%, p < 0.01) but not ACBS. After adjustment for extent of disease and other potential confounders, ethnic groups differed marginally in receipt of PTCA but not ACBS, while gender differences were not significant. Although women received revascularization procedures less frequently than men, this difference did not persist after controlling for extent of coronary artery disease by angiography: therefore, these observed differences in delivery of health care services may be appropriate. Mexican Americans received PTCA, but not ACBS, less frequently than NHW. This selective ethnic difference in receipt of PTCA does not appear to be associated with the extent of disease or other medical characteristics, and may represent inappropriate bias in delivery of health care services.

Perception of the medical risk of spaceflight.

We conducted an opinion survey to improve the characterization of medical risk during spaceflight, using a questionnaire designed to elicit space medicine experts' perceptions of the probability, health effect, and mission impact of selected medical events occurring during spaceflight missions of 30-90 d. This questionnaire was directed toward those events about which little data currently exist, therefore medical events that have occurred during spaceflights with some frequency, such as space motion sickness, were excluded from the questionnaire. The questionnaire was mailed to 99 clinical and research professionals involved with NASA medical programs; 65 responses were returned, of which 60 could be analyzed. The experts rated skin disorders as the most likely to occur, but which would have little effect on mission completion or astronaut health. Circulatory diseases were rated as having the lowest probability of occurrence, but the highest effect on the mission or on a crewmember's health. The results of this survey will be combined with data from analogous populations and existing astronaut health data to establish a data set to support decisions about allocation of health care resources.

Higher levels of social support predict greater survival following acute myocardial infarction: the Corpus Christi Heart Project.

Although low levels of social support have been related to mortality from coronary heart disease, little is known about the role of social support among Mexican Americans. The authors therefore examined the relationship between social support and long-term survival in the Corpus Christi Heart Project. They developed a social support scale that used data collected during in-hospital interviews of 292 Mexican Americans and 304 non-Hispanic Whites who survived a myocardial infarction for more than 28 days. The scale incorporated three measures: marital status; if not married, whether living alone; and whether advised to seek help. During an average follow-up period of 43 months, 115 participants died. Survival following myocardial infarction was greater for those with high or medium social support than for those with low social support. With age, gender, ethnicity, education, employment, smoking, diabetes, hypertension, and hypercholesterolemia included in a proportional hazards regression model, the relative risk of mortality was 1.89 (95% CI, 1.20-2.97) for those with low social support. But when the two ethnic groups were analyzed separately, low social support was no longer a significant predictor of mortality for non-Hispanic Whites, whereas for Mexican Americans, the relative risk of mortality was 3.38 (95% CI, 1.73-6.62) for those with low social support.

The relation of diabetes to the severity of acute myocardial infarction and post-myocardial infarction survival in Mexican-Americans and non-Hispanic whites. The Corpus Christi Heart Project.

The effect of diabetes on survival after myocardial infarction (MI) was examined in a prospective population-based study of individuals hospitalized with MI in a bi-ethnic community of Mexican-Americans and non-Hispanic whites. Among Mexican-Americans, 54% (331 of 610) had diabetes compared with 33% (192 of 589) of non-Hispanic whites (P < 0.001). Among those with diabetes, the prevalence of a history of a cardiac event before the index admission was significantly higher (odds ratio = 1.4, 95% confidence interval [CI] 1.1-1.8) than among nondiabetic subjects. During the index hospitalization, diabetic subjects received cardiac catheterization less frequently than did nondiabetic subjects (45.1 vs. 51.5%, P = 0.03). Diabetic subjects had lower estimated ejection fractions, and the number of coronary arteries with significant obstruction (> 75%) was higher (P < 0.001). The peak creatine phosphokinase and creatine phosphokinase myocardial isoenzyme (CK-MB) levels were similar in diabetic and nondiabetic subjects. Despite a similar infarct size, diabetic subjects had a higher incidence of congestive heart failure (relative ratio = 2.2, 95% CI 1.7-2.8), more adverse indexes of short-term and long-term prognosis, and a longer average hospital stay (12.1 vs. 8.9 days, P < 0.01). After adjustment for age, sex, and ethnicity, the cumulative risk for total mortality, over 44 months of follow-up, was 37.4% among diabetic compared with 23.3% among nondiabetic subjects (P < 0.001). Diabetic subjects had a higher 28-day case-fatality rate post-MI as well as higher long-term mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Body fat distribution in men and women of the Hispanic health and nutrition examination survey of the United States: associations with behavioural variables.

Body fat distribution is a biological risk factor for cardiovascular disease and diabetes. There are known genetic factors influencing body fat distribution, but variation in this characteristic is also attributable to human behavioural and socioeconomic variables such as social class. Björntorp has proposed that these associations may be due to a series of physiological responses to psychosocial stress, most prominently chronic stimulation of the adrenal-cortical system. This system is known to affect body fat distribution. Elsewhere we have shown that general socioeconomic status is related to body fat distribution in men and women of the Hispanic Health and Nutrition Examination Survey (HHANES) of the United States. In this paper we explore the relationship with those behavioural variables available from the HHANES which could hypothetically serve as indicators of psychosocial stress: smoking, drinking and depression. For both sexes in all Hispanic ethnic groups except Puerto Rican men, as socioeconomic status declined, subcutaneous fat became more centrally distributed. This relationship continued to be significant after controlling for the behavioural variables. A positive relationship was also found between smoking and central body fat distribution which was independent of socioeconomic status. This relationship was statistically significant for all subsamples except Cuban-American women. No consistent relationships were found between body fat distribution, drinking and depression. The data support the hypothesis that body fat distribution may be linked to the social stress of low socioeconomic status, independent of the behavioural factors tested.

Mortality after hospitalization for myocardial infarction among Mexican Americans and non-Hispanic whites: the Corpus Christi Heart Project.

We compared short- and long-term mortality among 334 Mexican Americans and 348 non-Hispanic whites hospitalized for myocardial infarction in the Corpus Christi Heart Project. Age-adjusted 28-day case fatality rates were 37% and 68% greater among Mexican-American women (6.7%) and men (6.2%) than among their non-Hispanic white counterparts (4.9% and 3.7%). Age-adjusted all-cause mortality rates over the next 25-month period, among those who survived the initial 28 days, were similar among Mexican-American and non-Hispanic white women (17.8% and 18.1%), but were 70% higher among Mexican-American men than among non-Hispanic white men (17.4% and 10.2%, respectively). Age-adjusted 25-month coronary mortality rates among initial 28-day survivors were 40% greater among Mexican-American women than among non-Hispanic white women (12.5% vs 9.0%), and 129% greater among Mexican-American men than among non-Hispanic white men (11.4% vs 5.0%, respectively). Thus, nearly all measures of post-myocardial infarction mortality indicated a survival disadvantage for Mexican Americans compared to non-Hispanic whites.

Hospitalization rates for myocardial infarction among Mexican-Americans and non-Hispanic whites. The Corpus Christi Heart Project.

The rate of hospitalization for myocardial infarction was examined in the Corpus Christi Heart Project (CCHP), a prospective population-based surveillance program in a biethnic community of Mexican-Americans and non-Hispanic whites. During 12 months of ascertainment, a total of 740 patients hospitalized with definite (217) or possible (523) myocardial infarction were identified. Of the 740 subjects, 334 were Mexican-Americans (150 females and 184 males), 348 were non-Hispanic whites (138 females and 210 males), and 58 were of other ethnic backgrounds. The 1-year age-adjusted rates of hospitalization per 100,000 population were 427.4 and 276.9 among Mexican-American and non-Hispanic white females, respectively, and 721.4 and 502.6 among Mexican-American and non-Hispanic white males, respectively. The age-adjusted hospitalization rate ratios for Mexican-Americans in relation to non-Hispanic whites were 1.55 (95% confidence interval [CI]: 1.23 to 1.95) and 1.40 (95% CI: 1.15 to 1.70) for females and males, respectively. These results suggest that Mexican-Americans may have a greater burden of coronary disease than non-Hispanic whites.

Which measure of body fat distribution is best for epidemiologic research?

Multivariate associations were sought between risk factor levels (total cholesterol, high density lipoprotein (HDL) cholesterol, triglycerides, glucose, and systolic and diastolic blood pressures) and two sets of anthropometric variables (four circumferences and six skinfolds) to select a set of anthropometric indicators of body fat distribution that correlate most highly with risk of disease. Subjects were men (n = 285) and women (n = 672) from a study of gallbladder disease in a Mexican American population in Starr County, Texas, 1985-1986. The canonical correlations showed that circumferences (0.49-0.61) and skinfolds (0.42-0.60) were equally well correlated to risk factor levels independently of sex and age. Weights from the canonical analyses suggest that measurements at or above the waist and on the lower limb (thigh) are most heavily loaded toward risk (waist = highest risk; thigh = lowest risk). The simplest and most reliable index of body fat distribution for both sexes is the ratio of waist to thigh circumferences. The more commonly used waist/hip ratio proved more valid in women, but not in men. Simple skinfold indices of body fat distribution were more poorly correlated to risk factor levels than the corresponding circumference ratios. In women, body mass index and waist circumference by themselves did as well as body fat distribution indices in explaining variation in risk factors, suggesting the involvement of visceral fat in the body fat/body fat distribution disease relation.

Body circumferences as alternatives to skinfold measurements of body fat distribution in Mexican-Americans.

The ratios of circumferences (waist/hip, waist/thigh) have been proposed in lieu of skinfold measurements for studies of obesity and body fat distribution. The purpose of this paper is to present our experience in measuring a series of body circumferences and skinfolds in an obese population, and seek the relationship between these two kinds of variables as indicators of fatness and body fat distribution using canonical correlation analysis. With this method, weighted vectors of circumferences on the one hand and skinfolds on the other, are formed in such a way that the correlation between the two sets of variables is maximized. The weights (regression coefficients) and their signs help us select the best combination of circumferences which describe a component of centralized obesity. Our experience showed that 21 percent of women would have been excluded from this multivariate analysis due to skinfolds what could not be measured (mainly due to poor fold definition). Few men were so excluded (6 per cent), and almost all circumferences could be measured in both sexes. A first canonical correlation was substantial (0.84 in women, 0.89 in men) and appeared to relate to level of fatness. A second canonical correlation was moderate (0.59 in women, 0.42 in men) and statistically significant (P less than 0.01) in both sexes. Only in women was it independent of age, but in both sexes it reflected differences in central and peripheral (especially lower limb) fat. The simple waist/thigh ratio correlated well with the second canonical variate (0.79 in women, 0.67 in men).(ABSTRACT TRUNCATED AT 250 WORDS)