High Altitude Associated With Lower Cardiovascular Disease Mortality Rates?
High Altitude Associated With Lower Cardiovascular Disease Mortality Rates?
Faeh D, Gutzwiller F, Bopp M; Swiss National Cohort Study Group
Circulation. 2009;120:495-501
Epidemiology studies of patients with end-stage renal disease (ESRD) have examined the comparative epoetin alfa requirements and mortality rates among patients at varying levels of altitude. These studies suggested that higher altitudes may confer a benefit. Additionally, multiple studies have also examined outcomes at a population level on the basis of altitude, including hypertension and hypercholesterolemia. This study conducted by Faeh and colleagues examined the association between altitude and mortality.
The Swiss National Cohort is a nationwide longitudinal research platform of record linkages that are based on data collected by the Swiss Federal Statistical Office. The core cohort was composed of 6.22 million residents from the 1990 census that could be satisfactorily linked to mortality or the 2000 census record. Of the 3 cultural groups in Switzerland (German 72%, French 23%, and Italian < 5%), the analysis was restricted to the German population to maximize power and limit heterogeneity. The final study population was composed of 1,641,144 people, contributing 14.52 person-years. Places of residence and birth were assessed in the 1990 census. Persons were coded as "moving up" if the places of residence were at least 200 m higher than their places of birth and, similarly, "moving down" if the places of residence were at least 200 m lower. The reference group consisted of those individuals who did not move more than 200 m in altitude in either direction.
The rates of mortality due to heart disease or stroke were calculated and stratified on the basis of sex and altitude. Among both men and women, the rates of stroke seemed to be lowest for those people who lived at the lowest and highest elevations. However, the rates of mortality due to heart disease appeared to have a more linear relationship to altitude. The rate of death due to heart disease for men decreased from 289 deaths/100,000 patients-years, 286 deaths/100,000 patients-years, and 290 deaths/100,000 patients-years at altitudes of < 300 m, 300-600 m, and 600-900 m to 273 deaths/100,000 patients-years at 900-1200 m, 246 deaths/100,000 patients-years at 1200-1500 m, and 242 deaths/100,000 patients-years at > 1500 m. Relative rates of change were similar for women.
Using Poisson regression, increasing altitude was associated with better outcomes in models of the outcomes of mortality related to heart disease and stroke separately. Examining the associations with mortality due to heart disease, a 1000-m increase in altitude was associated with a relative risk (RR) of 0.78 (P < .001). However, moving to a higher altitude from that of one's birthplace was associated with an RR of 1.08 (P < .001), and moving down was associated with an RR of 0.96 (P = .007). The relationship between altitude and mortality due to stroke was similar but not as strong. A 1000-m increase in altitude was associated with an RR of 0.88 (P = .002). Moving up from birth to the 1990 census was associated with an RR of 0.94 (P = .106), and moving down was associated with an RR of 0.93 (P < .001).
The associations between cardiovascular disease mortality rates and altitude raise 2 important considerations. First, they strongly support the notion that altitude plays an important role in cardiovascular health. Not only does current altitude predict outcome, but relative to the other individuals at that altitude, if a patient moved up (ie, spent time at a lower altitude prior to the move), that patient would have slightly poorer outcomes. Similarly, if one moved down (ie, spent time at a higher altitude prior to the move), the subject would have slightly better outcomes compared with others at their current altitude. This is a "dose-response" relationship of sorts. Second, the association noted in the study also adds to a growing understanding of the factors that influence the mortality of patients with ESRD. The demonstration of these associations in a population-based cohort suggests that the mechanism is more universal than the specific metabolic and functional alterations specific to kidney disease. In our continued search for mechanisms to reduce the mortality risk for patients with ESRD, this is indeed important information.
Abstract
Lower Mortality From Coronary Heart Disease and Stroke at Higher Altitudes in Switzerland
Faeh D, Gutzwiller F, Bopp M; Swiss National Cohort Study Group
Circulation. 2009;120:495-501
Summary
Epidemiology studies of patients with end-stage renal disease (ESRD) have examined the comparative epoetin alfa requirements and mortality rates among patients at varying levels of altitude. These studies suggested that higher altitudes may confer a benefit. Additionally, multiple studies have also examined outcomes at a population level on the basis of altitude, including hypertension and hypercholesterolemia. This study conducted by Faeh and colleagues examined the association between altitude and mortality.
The Swiss National Cohort is a nationwide longitudinal research platform of record linkages that are based on data collected by the Swiss Federal Statistical Office. The core cohort was composed of 6.22 million residents from the 1990 census that could be satisfactorily linked to mortality or the 2000 census record. Of the 3 cultural groups in Switzerland (German 72%, French 23%, and Italian < 5%), the analysis was restricted to the German population to maximize power and limit heterogeneity. The final study population was composed of 1,641,144 people, contributing 14.52 person-years. Places of residence and birth were assessed in the 1990 census. Persons were coded as "moving up" if the places of residence were at least 200 m higher than their places of birth and, similarly, "moving down" if the places of residence were at least 200 m lower. The reference group consisted of those individuals who did not move more than 200 m in altitude in either direction.
The rates of mortality due to heart disease or stroke were calculated and stratified on the basis of sex and altitude. Among both men and women, the rates of stroke seemed to be lowest for those people who lived at the lowest and highest elevations. However, the rates of mortality due to heart disease appeared to have a more linear relationship to altitude. The rate of death due to heart disease for men decreased from 289 deaths/100,000 patients-years, 286 deaths/100,000 patients-years, and 290 deaths/100,000 patients-years at altitudes of < 300 m, 300-600 m, and 600-900 m to 273 deaths/100,000 patients-years at 900-1200 m, 246 deaths/100,000 patients-years at 1200-1500 m, and 242 deaths/100,000 patients-years at > 1500 m. Relative rates of change were similar for women.
Using Poisson regression, increasing altitude was associated with better outcomes in models of the outcomes of mortality related to heart disease and stroke separately. Examining the associations with mortality due to heart disease, a 1000-m increase in altitude was associated with a relative risk (RR) of 0.78 (P < .001). However, moving to a higher altitude from that of one's birthplace was associated with an RR of 1.08 (P < .001), and moving down was associated with an RR of 0.96 (P = .007). The relationship between altitude and mortality due to stroke was similar but not as strong. A 1000-m increase in altitude was associated with an RR of 0.88 (P = .002). Moving up from birth to the 1990 census was associated with an RR of 0.94 (P = .106), and moving down was associated with an RR of 0.93 (P < .001).
Viewpoint
The associations between cardiovascular disease mortality rates and altitude raise 2 important considerations. First, they strongly support the notion that altitude plays an important role in cardiovascular health. Not only does current altitude predict outcome, but relative to the other individuals at that altitude, if a patient moved up (ie, spent time at a lower altitude prior to the move), that patient would have slightly poorer outcomes. Similarly, if one moved down (ie, spent time at a higher altitude prior to the move), the subject would have slightly better outcomes compared with others at their current altitude. This is a "dose-response" relationship of sorts. Second, the association noted in the study also adds to a growing understanding of the factors that influence the mortality of patients with ESRD. The demonstration of these associations in a population-based cohort suggests that the mechanism is more universal than the specific metabolic and functional alterations specific to kidney disease. In our continued search for mechanisms to reduce the mortality risk for patients with ESRD, this is indeed important information.
Abstract