Climate change could increase congenital heart defects

As climate change makes extreme heat more likely–like the 120-degree days in parts of Australia this January, or record-breaking heat that killed dozens of people in Japan and Canada last summer–it also may be doing internal damage to our bodies. A new study looked at how heat waves in the U.S. in the near future could be linked to thousands of babies born with abnormal hearts.

“We expect that pregnant women, because of climate change, will be exposed to more extreme heat in the next 10 years or 20 years,” says Shao Lin, a public health professor at the University of Albany, New York and one of the authors of the paper, which was published today in the Journal of the American Heart Association. In a previous study, Lin linked extreme heat early in pregnancy–when the baby’s heart is developing–to congenital defects. In the new paper, researchers projected future temperatures in eight regions of the U.S. between 2025 and 2035, and then calculated how many more defects might occur as heat increases.

The researchers looked at eight states where federal data is available about congenital defects. As they studied extreme heat, they looked at how many days were likely to be hotter than the 90th or 95th percentile for that region, and how long and frequent future heat waves might be. In the states they studied, they found that an additional 7,000 babies might be born with defects over a decade. The risk of defects is highest when pregnant women are exposed to excessive heat in the spring, perhaps because they may be more likely to be inside in air conditioning in the summer.

“This is part of the population most people don’t think is vulnerable to heat,” says Lin. “Most people think about how climate change will [impact] the elderly or children, but pregnant women have been ignored as a vulnerable population. So we want to put the message out.” There are additional health risks; in another study, for example, Lin found exposure to extreme heat later in pregnancy can also make it more likely that babies are born with low birth weight.

The researchers looked at the near future in order to have the most accurate results. But as the planet keeps heating up, the health risks will grow. Each small shift in climate leads to a dramatic increase in the frequency of extreme heat waves. One study found that by the middle of the century, population exposure to days hotter than 95 degrees may grow five or six times.