Wouldn't it be great if you could circle a date on your calendar and have your period actually show up then? You'd plan beach trips around it and you'd never be caught without a tampon. Unfortunately, a little variation is typical: "The average cycle is 28 daysthat's 28 days between the first day of one period and the first day of your next periodbut anywhere in between 24 and 31 days is considered normal," says Veronica Lerner, MD, assistant professor of obstetrics and gynecology at NYU Langone Medical Center. "Still, a highly irregular period is usually a sign that something else isn't right in your body." Take note of these 10 things that could be messing with your menstrual cycle, and see your doc if anything seems too far off.
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Heard of marathon runners losing their periods? It's not a myth: frequent rigorous exercise combined with low body fat puts stress on your body, and this stress tells your brain to stop producing reproductive hormones. "Since you can't nourish a baby under extreme stress, your body temporarily shuts down the production of fertility hormones," explains Dr. Lerner. One study found that half of exercising women experience subtle menstrual irregularity. A period that arrives a few days off schedule is nothing to worry about, but see your doctor if you haven't had your period for longer than three months. "It's a condition called amenorrhea, and it can compromise your bone density long-term," says Dr. Lerner.
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Carrying extra pounds does more than sabotage your skinny jeans. "Excess fat cells result in elevated levels of estrogen, which can ultimately stop your ovaries from releasing an egg," says Dr. Lerner. Meanwhile, the endometrial lining continues to thicken. "Obese women usually experience heavy, infrequent, longer-lasting periods." If you're overweight and experiencing these symptoms, don't just stock up on "super" tampons. Having too much estrogen for an extended period of time increases your risk of endometrial cancer. If you can't seem to drop pounds, talk to your gynecologist about going on the pill. "Birth control thins out your endometrial lining, decreasing your risk for endometrial cancer," explains Dr. Lerner.
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Your body has the opposite reaction when you're underweight; it doesn't produce enough estrogen. "And you need adequate levels of estrogen to build your uterine lining and have a period," says Holly Puritz, MD, and medical director of OB/GYN services at Sentara Leigh Hospital in Virginia. Still, if you've always weighed less than average, this might not be a problem. "You're more likely to notice a difference if you've lost a significant amount of weight in a short period of time," Dr. Puritz explains. If you've dropped serious pounds, but you're still within a healthy range, your body should adjust within a few months.
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Taking prescription drugs
Any medication that involves hormoneslike thyroid medication (and thyroid problems in general), steroids, or antipsychotics (which release a hormone, dopamine)can influence your period. The first thing you should know is that hormones don't act in isolation. "All hormones circulate throughout your bloodstream, so they're all connected, even if they're produced in different glands," says Dr. Puritz. Plus, some hormone receptors look a lot like other hormone receptors, so a drug can easily mistake its target hormone, affecting a fertility hormone as well as the intended thyroid hormone, for example. Don't panic if your cycle is a couple days off, but see your doc if your period is consistently over a week early or late.
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Working with pesticides
"Pesticides mimic hormones," says Dr. Puritz. "They compete with and block the hormones in your body, making it difficult for your endocrine system to function properly." One study found that women living on farms that used pesticides had longer cycles and more missed periods than women who lived on pesticide-free farms. What's more, those who were exposed to hormonally active pesticides were 60 to 100% more likely to have long cycles, missed periods, and spotting, according to the study published in the American Journal of Epidemiology. Dr. Puritz suggests limiting your exposure any way you can: "Even choosing organic food at the supermarket helps," she says.
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Feeling stressed out
"Evolutionarily speaking, times of high stress aren't conducive to bringing a baby into the world, and a regular cycle is designed to do just that," says Dr. Puritz. That explains why stressed out women were less likely to conceive than their more zen counterparts in a Human Reproduction study.
"Many people go on birth control pills to make their periods regular," says Dr. Lerner. "But it takes your body a few months to adjust." As the lining of your uterus gradually becomes thinner, you may see some spotting in between periods. Give your birth control two to three months before giving up in the name of irregularly. Then, if you still see spotting, make sure you're taking the pill at the exact same time everyday. "The pill stabilizes the lining of your uterus, but the lining needs a steady supply of hormones in order to stay put," says Dr. Puritz. That's why you bleed when you take the placebo pills at the end of the monththere's nothing stabilizing the lining anymore. If you wait longer than 24 hours before taking your next pillsay you usually take it at 10:00am everyday, and you suddenly take it at 1:00pm one dayyou may notice some unexpected spotting.
While you probably expect your periods to become less frequent as you approach menopause, it can throw some surprises at you. Thanks to shifts in your hormones, your cycle gets shorter before it gets longer, explains Samantha Butts, MD, associate professor of obstetrics and gynecology at Penn Medicine. "Then, at a certain point, the number of eggs in your ovaries declines such that your periods are infrequent," she says. Unfortunately, that means you'll need to put up with more frequent periods before you can start saying goodbye for good. Until menopause comes, may we suggest stocking up on chocolate and keeping an emergency tampon in your purse?
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You know skimping on sleep can make you feel off, but subpar slumber patterns can throw off your cycle, too. In fact, people who work irregular hours (like nurses and flight attendants) are more likely to experience irregular periods, according to a review published in Sleep Medicine. "Shifting your body clock affects your reproductive hormones, which influence ovulation and menstruation," says Fiona Baker, PhD, program director of SRI International's Human Sleep Research Laboratory, and author of the review. Plus, irregular sleeping patterns make your melatonin levels wonky (melatonin has been shown to affect reproduction and menstruation in animals). If you're stuck working the night shift, Baker suggests using blackout curtains and earplugs to help you sleep well when it's light out.
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Traveling across time zones
Your brain produces the hormone melatonin to signal to your body that it's time to go to bed. But when you travel to another time zone, your body releases melatonin as if you're still at home, even if it's broad daylight in your new location. In order to adjust to the new schedule, your body suppresses the hormone until it's dark again. These fluctuations aren't good for your flow: "It's probably not a big deal if you're traveling once in a while, but these adjustments can throw off your cycle if they're happening regularly," says Baker. Really rackin' up those frequent flyer miles? Try these tips for beating jet lag.