A recent study showed that the COVID-19 vaccines may temporarily alter menstrual cycles. After vaccination, participants in the study noticed an increase in the length of their menstrual cycles by about one day, on average. In subsequent cycles, however, the length of their menstrual cycles decreased by a day—confirming that the vaccines have little effect on menstrual cycles.
Fluctuations of up to eight days in a menstrual cycle are considered normal, and a normal menstrual cycle is 21 to 35 days long, with a period that lasts two to seven days. In fact, there are many factors that can cause a menstrual cycle to fluctuate, says Page Animadu, M.D., an obstetrician and gynecologist at Henry Ford Health. But why could the COVID-19 vaccines cause a slight fluctuation?
“There has been so much media attention around the COVID-19 vaccines, so for some people, getting vaccinated might make them stressed, and stress can affect menstrual cycles,” says Dr. Animadu. “The vaccines can also cause flu-like symptoms (such as body aches, fatigue and fever) and getting the flu or a cold can temporarily cause a change in your menstrual cycle. These are the two theories as to why the vaccines might have a small, short-lived effect on the length of your menstrual cycle.”
Other factors that can cause your menstrual cycle to fluctuate include:
- Stress. When you’re stressed out, your cortisol level increases, which could tell your brain to stop making certain hormones that cause you to ovulate. “Really, anything that causes stress on the body can temporarily cause a change in your menstrual cycle,” says Dr. Animadu.
- Contracting an illness. “When your body is trying to heal itself from an illness—whether a cold or the flu, for example—it’s not going to use its energy to maintain fertility, it’s going to use its energy to maintain major organ functions like your heart, liver and kidneys,” says Dr. Animadu.
- Gaining too much weight. Adipose tissue (commonly known as body fat) makes estrogen, and estrogen builds the lining of the uterus. When you have too much body fat, it can lead to an excess of estrogen, thickening the uterus so much that it continuously sheds (i.e., bleeds), as it is constantly being stimulated from adipose tissue. This can cause you to have heavy, long periods. “More than 30% of reproductive-age women are considered obese, so this is something that a lot of women struggle with,” says Dr. Animadu. “The good thing is that losing 7% of weight can bring you back to a normal cycle.”
- Losing too much weight. On the flip side, losing too much weight can make you lose your period. This is called amenorrhea, and it can be a sign of an eating disorder. “When your body isn’t getting the nutrients and energy it needs, it will start shutting off inessential processes—it won’t waste energy on fertility,” says Dr. Animadu. “Getting enough calories and eating a well-balanced diet is important to maintaining a regular cycle.”
- Exercising excessively. Exercising too much can also lead to irregular periods. This is because your body doesn’t have enough energy to ovulate—and ovulation is what causes you to have a period.
- Eating a diet high in soy. Just as excess body fat leads to estrogen dominance and can cause heavy, long periods, eating a diet high in soy—a food that contains estrogen—can also make your periods heavier and longer. If this is true for you, try eliminating soy from your diet.
Changes in your menstrual cycle can become an issue if:
- Your periods have been heavier than normal for three consecutive months or your periods have lasted for more than 7 to 10 days for three consecutive months.
- You’ve gone three consecutive months without a period or your period lasts less than a day or two for three consecutive months.
“These are all indications that you should see your OBGYN to determine why your cycle is acting out of the ordinary,” says Dr. Animadu. “There could be an underlying medical issue, such as a thyroid or other hormone disorder. And if you aren’t doing so already, tracking your period each month is a really good way to ensure your cycle is normal. Having a regular menstrual cycle is an indication of health, so if you’re having major irregularities, it could be the first indication that something is wrong.”
Subscribe to receive a weekly email of our latest articles.
Dr. Page Animadu is an obstetrician and gynecologist who sees patients at Henry Ford Medical Center – New Center One.