• Researchers have identified a link between hot temperatures and weight loss in heart failure patients, indicating that their condition has worsened.
  • The scientists used data from France during the 2019 heatwave, finding an association between the hot weather and a weight loss of 1.5kg.
  • 1,420 patients with chronic heart failure took part in the study, with the median age of the participants being 73.

Scientists have discovered that hot temperatures were closely linked with weight loss in heart failure patients during the 2019 heatwave in France.

Study author, Professor François Roubille of Montpellier University Hospital, France, said: “The finding is timely given the heatwaves again this year. The weight loss we observed in people with heart failure may lead to low blood pressure, especially when standing up, and renal failure, and is potentially life-threatening.

“With rising temperatures forecast for the future, clinicians and patients should be ready to reduce the dose of diuretics when weight loss occurs.”

In patients with heart failure, the heart does not efficiently pump blood around the body. Due to this, waste products accumulate in the body, leading to shortness of breath and fluid build-up in the lungs, legs and abdomen.

Fluctuations in weight can be dangerous in people with chronic heart failure because weight changes can lead to hospitalisation for lung congestion. Therefore measuring weight is a vital part of monitoring the condition.

Water pills called diuretics are used to treat congestion by increasing urine output and reducing breathlessness and swelling. Current ESC guidelines recommend educating patients to increase their diuretic dose or to notify their healthcare team if they experience symptoms of breathlessness, swelling, or rapid and unexpected weight gain of over 2kg in three days. However, weight loss has not received the same amount of attention.

The authors behind the current study hypothesised that patients with heart failure would have changes in body weight during a heatwave. Professor Roubille explained: “When healthy people drink more fluids during hot weather, the body automatically regulates urine output. This does not apply to patients with heart failure because they take diuretics.”

Researchers examined the association between body weight and air temperature in France between the 1st of June and the 20th of September, covering the occurrence of two heatwaves – one at the end of June and the other at the end of July. Throughout most of the country, temperatures exceeded 32°C on the 26th of June.

1,420 patients with chronic heart failure were included in the study; the median age of the participants was 73, with the average weight being 78kg, and 28% of the patients were women. Overall, the cohort was from 68 counties, representing over 71% of the French territory.

Using a national telemonitoring system, information on weight and symptoms was obtained remotely. Patients weighed themselves daily, using a weighing scale that automatically sent measurements to the clinic.

Symptoms including oedema, fatigue, breathlessness and cough were reported by answering questions on devices such as a smartphone or tablets, with answers also sent automatically to the clinic.

Noontime daily temperatures were taken using data from the weather station closest to each patient’s home.

Researchers then analysed the association between each patient’s weight, the ambient temperature on the same day, and the temperature two days before the weight measurement.

The relationship between temperature and weight was ‘very strong’ with weight dropping as the temperature rose. This relationship was strongest two days before the weight measurement. With a mean weight of 78kg, a variation of 1.5kg was identified during this short period.

Professor Roubille continued: “The weight loss we observed during the heatwave was clinically relevant. Patients weighing 78 kg lost 1.5 kg in a short period of time. We were surprised to see that weight dropped with hot temperatures, as we had expected the opposite. For this reason, the telemonitoring system was programmed to alert clinicians when patients gained weight.”

With heatwaves becoming more frequent, Roubille believes telemonitoring systems should also alert clinicians if a heart failure patient loses weight.

“Systems could notify patients losing weight that it may be due to the heat and they should contact their healthcare provider about reducing the dose of diuretics. For heart failure patients not monitored remotely, a good rule of thumb would be to contact a healthcare professional if weight drops by 2 kg during a heatwave for advice on adjusting diuretic medication. Reacting early should help us to prevent complications,” Roubille concluded.

This study is published in ESC Heart Failure.

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