Heat and heart disease is unhealthy combination.

Aug 08, 2012

Wilker, EH, G Yeh, GA Wellenius, RB Davis, RS Phillips and MA Mittleman. 2012. Ambient temperature and biomarkers of heart failure: a repeated measures analysis. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1104380.



Synopsis by Kai Zhang and Wendy Hessler

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An uptick in the body's defense system may explain why congestive heart failure worsens as temperatures climb. When it's hotter, inflammation – the body's response to stress or harm – can increase and lead to more severe symptoms in those who already have the cardiac problem, report researchers. This is the first study to look at the link between temperature and inflammation in those with heart disease and suggests people with congestive heart failure should avoid the heat.

 

 

Context

Temperatures are expected to increase with a warming climate. In addition, heat waves are projected to be more frequent, more intense and longer as a consequence of climate change.

Heat is estimated to be the number one weather-related killer in the United States. It is associated with increased risk of death, hospital admissions, heat stroke, heat exhaustion, cardiovascular diseases and respiratory diseases.

Hot weather does not affect everyone's health equally. Those vulnerable to heat-related death and illness include adults with existing heart and other chronic disease; athletes; the elderly; children; the mentally ill; racial/ethnic minorities; and the poor.

Weathermen and researchers often use apparent temperature to indicate how hot it is outside. The apparent temperature refers to the perceived temperature – how hot it actually feels – and is based on the measured temperature and humidity.

Cardiovascular disease is a leading cause of death in the United States. However, little is known about the underlying physical mechanisms between heat and cardiovascular diseases, including congestive heart failure.

Patients diagnosed with congestive heart failure (or just heart failure) have problems efficiently pumping blood to meet the body’s need. Heart disease and diabetes can contribute to the heart failure. While there is no cure, the condition can be stabilized with medication and lifestyle changes. It is known that people with heart failure are more vulnerable to recurrence, especially during hot weather.

Inflammation is the first response of the immune and hormone systems to injury and stress by often releasing extra proteins. Measuring these proteins and other releases indicates the extent and severity of the injury. These same markers are associated with episodes in heart failure patients.

What did they do?

The study examined the associations between temperature variations and the changes in heart disease markers in the blood of participants who were diagnosed with cardiovascular problems.

Researchers recruited 100 patients aged 34 to 96 from several walk-in clinics in and around Boston. The participants were 64 percent male and 86 percent were white. They were being treated for congestive heart failure and had impaired heart muscle function.

The heart failure patients in this study were selected because they have conditions that make them vulnerable to excessive heat.

The researchers measured the levels of several inflammation markers in the participants' blood samples that were taken at the first meeting and again at 6 and 12 weeks. These markers include B-type natriuretic peptide (BNP), a hormone that indicates heart muscle damage and inflammation; and C-reactive protein (CRP) and tumor necrosis factor, two indicators of systemic inflammation and impaired immune function.

They also measured temperature and other weather conditions and then calculated the apparent temperature - a measure of temperature and humidity that represents how hot it feels. Because temperatures can vary throughout the day and from day to day, researchers calculate and compare them using a moving average. Temperatures on the day of a patient's visit and two or three days before that visit are averaged to reflect the exposure of a patient to temperature over a short-term period. For instance, the calculated temperature value for a patient's visit would be the average of the day of the vist, one day before the visit and two days before the visit.

They also assessed a number of factors that might affect the association, including particulate matter, ozone, exercise, season and gender.

What did they find?

The most important finding was that higher apparent temperatures were associated with higher levels of inflammation in the patients with preexisting heart health conditions. That is, the higher the temperature, the higher the levels of biomarkers in the blood of these patients with heart failure problems.

In particular, they report a 10 percent increase in the protein BNP and a 20 percent increase in CRP in patients with a 9 degree Fahrenheit increase in the average apparent temperatures over 3 or 4 days. This increase was just half of the daily apparent temperature variation during the study period. No association between tumor necrosis factor and ambient temperature and was found.

Similar conclusions were found between each blood marker and temperature when they considered pollution, exercise, season and gender.

What does it mean?

Elevated temperature can trigger heart attacks and other cardiovascular problems in people being treated for heart disease. For the first time, this study identifies a possible explanation for how temperature can cause heart failure.

This study covered a broad temperature range – from 12 to 81 degrees Fahrenheit – and did not include heat waves. The health effects of high temperature during extreme hot days are expected to be more severe.

The findings suggest that high temperatures increase heat stress in the body. The stress then changes underlying physiological responses related to inflammation and cell injury. These responses result in heart failure by increasing damage to heart tissue and inflammation.

This is the first study to look at a potential mechanism between temperature and heart failure by measuring protein indicators related to heart disease in patients with cardiovascular disease.

The findings are relevant for public health prevention. The results suggest that those with heart failure risk should avoid the high temperatures that occur during the hotter summer months. The study will also be important as temperatures rise due to climate change.

One key limitation of the study is that the enrolled participants had heart failure and systolic dysfunction – problems with the heart's ability to contract and properly pump blood through the body. Thus, this finding may not apply to people with other types of cardiovascular diseases.

Resources

Meehl, GA and C Tebaldi. 2004. More intense, more frequent, and longer lasting heat waves in the 21st century. Science 305: 994-997.

National Weather Service. 2005. Heat: A major summer killer.

O’Neill, MS, DK Jackman, M Wyman, X Manarolla, CJ Gronlund, DG Brown, SJ Brines, J Schwartz and AV Diez Roux. 2010. U.S. local action on heat and health: Are we prepared for climate change? International Journal of Public Health 55(2):105-12.

Kovats, RS, and S Hajat. 2008. Heat stress and public health, a critical review. Annual Review Public Health 29: 41-55.

 

 

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