Too many caffeine-fueled late-night study sessions have adverse lifelong affects on a person’s body, said Harvard Medical School sleep expert Dr. Atul Malhotra yesterday.

Failing to get the recommended eight or nine hours of sleep each night correlates with documented health risks, Malhotra said at the Kessler Library at Brigham and Women’s Hospital during an event part of Sleep Awareness Week.

Citing a 2003 long-term study of more than 70,000 women, those who slept only five hours each night were more than 70 percent likely to have a heart attack than people who had a regular night of sleep. Women who only slept five hours also gained weight during the study at a rate 50 percent higher than those who slept more.

Staying awake for 18 hours could impair a person’s cognitive ability as much as an alcoholic drink, and after being awake for 24 hours, a person’s cognitive ability decreases to a level equivalent of being legally drunk, Malhotra said.

For those who get used to keeping late hours, their bodies are not adapting to their lack of sleep, he noted; rather, they are simply growing into a bad habit.

“We lose the ability to perceive how sleepy we are,” he said.

And although people who routinely burn the midnight oil during the week often think they can make up for their lack of sleep by catching up on it during the weekends, Malhotra said it is not enough.

“[It] probably helps a little bit, but you’d be foolish to think that would correct the problem,” he said.

Malhotra said people with sleeping problems should not rely on over-the-counter drugs to help them sleep and should avoid activities hindering sleep, such as late-night exercising, eating or consuming caffeine.

“I recommend no caffeine,” he said. “At the very least, don’t drink [coffee] after noon.”

Following the 2 p.m. lecture, the library served pastries and coffee.