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Soon it will be time to pack away the swimsuits and pull out the sweaters. Whether or not you’re on the pumpkin spice bandwagon, seasonal changes can affect more than what’s in your closet or what’s on the menu.

We asked resident expert Dr. A. Nicky Hjort, M.D., OB-GYN how the transition from summer to fall will affect our cycles. While there aren’t direct links between the angle of the Earth’s tilt and Aunt Flo, Dr. Hjort says the lifestyle changes that result from seasonal transitions can have a real effect on menses—and not necessarily in a good way.

01. You may get moodier.

In the warmer, sunnier seasons of spring and summer, we tend to get more exposure to sunlight, which is enables our bodies to produce more vitamin D and more dopamine, both of which are associated with positive moods and feelings of pleasure. Less sunlight can lead to seasonal affective disorder (SAD), which is characterized by symptoms of depression—among them sadness, loss of interest in things you used to enjoy, feelings of hopelessness, and craving and consuming more carbohydrates.

When it’s nice out, we also tend to spend more time outdoors and more time moving. Women who exercise regularly and who have a higher level of fitness are less likely to suffer from a severe form of PMS, aka premenstrual dysphoric disorder (PMDD), and are less likely to have heavy and irregular menstrual bleeding.

While these factors are certainly related, Dr. Hjort says it’s a case of the chicken and the egg. Does the sunlight, the exercise, or a combination of the two make us more enthusiastic about being more active over the summer? Whatever the case, a more active lifestyle usually means a more regular cycle. Try a workout you can do without having to leave the coziness of home.

02. Your cycles may get heavier or longer.

Dr. Hjort notes that the average American puts on three to ten pounds in the winter months. The causes are many—we overeat at the holidays, we don’t get out and exercise as much, and so on. Some of us shed those pounds when the weather transitions again, but not everyone does. While we can’t necessarily blame weight gain on the season, Dr. Hjort says there is a direct connection between weight gain and heaviness and length of cycle flow. How much of a gain will cause a noticeable difference differs from woman to woman, explains Dr. Hjort, but there is a point at which an unhealthy body mass index (BMI) will affect any woman’s cycle.

03. You may have less patience for unpleasant symptoms.

Because the connections between seasonal changes and our cycles are indirect, but related, Dr. Hjort suggests it’s possible that we simply have better tolerance for our cycles in months when we are enjoying ourselves more. When you’re eating al fresco, wearing flowing clothes, and looking forward to vacation and travel, less severe symptoms may seem more manageable. When the days are shorter and your commute feels like a trip to the Arctic, symptoms like cramps and blemishes on your skin will definitely be getting more of your annoyed attention.

Being aware of how your choices change with the seasons means you can take steps to counteract potentially negative side effects when Aunt Flo pays her holiday visits. As Dr. Hjort says, it’s not the seasons that affect our cycles, but what the seasons mean for our lifestyles that creates change. By making an effort to eat healthy, exercise regularly, go outside, and keep perspective on the little things that bring you joy, you may not notice changes in your cycle before the days lengthen again. So take a (cold) hard look at your typical fall and winter lifestyle and slowly make healthy habits that stick . . . and snow on, snow forth.

Photo Credit: Elissa Voss Photography