Please answer a question about the following article about Daylight saving time:

Opponents argue that actual energy savings are inconclusive, that DST increases health risks such as heart attack, that DST can disrupt morning activities, and that the act of changing clocks twice a year is economically and socially disruptive and cancels out any benefit. Farmers have tended to oppose DST.

What major health risk do people who oppose DST say it increases?
heart attack