We asked an ob-gyn to explain.

Sophie Turner's Game of Thrones character, Sansa Stark, overcame plenty of challenges throughout the show’s eight seasons (think being orphaned, held prisoner, regularly tortured, and more). But off-screen, Turner was fighting battles of her own, including a struggle with body image.

In a recent interview with The Sunday Times, Turner said that starring in GoT as a teen, during her “most awkward, uncomfortable, unsure-of-yourself years,” took a serious toll on her mental and physical health. In fact, she got to a point where her diet was so restricted that she lost her period, a condition called amenorrhea.

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Turner, who was 13 when she started working on GoT and is now 23, told the outlet: “Suddenly, everyone’s metabolism slows down at 17, 18 and then that’s documented. My skin and everything. People commenting on it. I was too aware of my body at a young age. And it just kind of took over my mind, it was all I would think about. Calorie counting, everything: ‘Oh, I’ll just eat nuts today.’”

She finally sought help when she was 19. “I stopped having my period for a year—that’s when I decided to have therapy,” she said. But how does that happen, exactly, and can extreme dieting play a role?

Why women lose their periods

Missing three or more menstrual periods in a row is called amenorrhea, according to the Mayo Clinic. There are two types of amenorrhea: primary amenorrhea, when a young woman never has a period in the first place, and secondary amenorrhea, when a woman does have a period that stops being regular, which seems to have been the case for Turner.

Christine Greves, MD, an ob-gyn at the center for obstetrics and gynecology at Orlando Health in Florida, tells Health that one reason a woman might lose her period could be hypothalamic amenorrhea—a condition in which the hypothalamus (a region of the brain) isn’t producing enough gonadotropin-releasing hormone (GnRH). This can be caused by a nutritional deficiency, extreme weight loss or stress, or too much exercise, she explains.

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GnRH regulates the hormones that make us menstruate, Dr. Greves says, so when levels of this hormone are low, a domino effect begins—causing a drop in other hormones, including estrogen, progesterone, and testosterone.

If your body thinks it might starve, she explains, it begins to prioritize survival rather than procreation, which is the purpose of menstruation. “If you’re stressed or not getting enough nutrients—if you think back to olden times, if you’re at war, et cetera—that’s not a time when resources are abundant,” she says. “So it’s probably not the best time to have a baby.”

What to do about it

Anyone who’s lost their period should speak with a doctor to determine the cause, Dr. Greves says. Besides the obvious issue—amenorrhea can cause infertility if a woman is trying to get pregnant—losing a period can be associated with other health risks, such as osteoporosis, according to the University of Rochester Medical Center.

If amenorrhea is related to diet, it’s important to work with a nutritionist, as well as a doctor, to come up with an eating plan that works for you. Once you’re regularly consuming sufficient calories and balanced nutrients—such as vegetables, fruits, whole grains, protein, and dairy—your period should resume.

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There’s no set number of calories or ratio of different foods a woman should be consuming in order to have a healthy menstrual cycle, however. Competitive athletes and women who exercise more than the average person will need to take in more calories, for example, while those who are less active will need fewer.

That’s why it’s key you work with a nutritionist or doctor to determine your needs, says Dr. Greves. “Try to make sure you’re getting adequate nutrients,” she advises, “and try to find healthy ways to manage your stress.”

Turner said therapy helped her recover, as did her now-husband, Joe Jonas. The two met when she was 20, and was still "very mentally unwell," she told The Sunday Times.

“He was, like, ‘I can’t be with you until you love yourself, I can’t see you love me more than you love yourself,’” Turner said. “That was something, him doing that. I think he kind of saved my life, in a way.”

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