Is the 28-Day Cycle A Myth? 

mbg Health Contributor By Gretchen Lidicker, M.S.
mbg Health Contributor
Gretchen Lidicker earned her master’s degree in physiology with a focus on alternative medicine from Georgetown University. She is the author of “CBD Oil Everyday Secrets” and “Magnesium Everyday Secrets.”

Image by Aaron Thomas / Stocksy

If you're a woman, you've almost definitely been told that 28 days is the "normal" cycle length. But ladies, is your cycle actually 28 days? And if it's not, is that something to worry about?  

According to a new study, the answers to these questions are most likely "no" and "no." In partnership with the recently FDA-approved contraceptive app Natural Cycles, researchers at the University College London analyzed more than 60,000 cycles—from about 125,000 women—and found that the 28-day cycle isn't actually the norm.

The results, which were published in Nature Digital Medicine, showed that only 13% of women have a 28-day cycle. Instead, the data showed that the average follicular phase—aka the days from the start of your period until ovulation—was about 16.9 days. The mean luteal phase—which is the time between ovulation and the start of your period was 12.4 days. And according to Sara Gottfried, M.D., that's OK. "The normal range for menstrual cycle is about 21 to 35 days. Twenty-eight days is simply the average," she says.

In fact, the results showed that only 65% of women had cycles that were between 25 and 30 days long. According to Jolene Brighten, N.D., naturopathic doctor and mbg Collective member, "Some women cycle every 26 days or every 32 days, and that is their normal. What matters more is what YOUR normal cycle is," she explains.

So is there any point when you should be worried about your cycle length? According to Brighten, regularity matters more than the actual length. "Women should be concerned and meet with their doctor if they have irregular or unpredictable cycles," she says.

That said, if your cycles are very short or very long, that might indicate an underlying health issue. As Brighten explains, "If your cycle is 21 days or less, this could indicate a luteal phase defect and insufficient progesterone. If your cycles are longer than 35 days, it's a good idea to discuss it with your doctor as this can be a sign of thyroid disease, androgen excess, and in some cases PCOS."

The data collected from this study will contribute to our knowledge base on menstrual cycles in a major way. As the study’s authors wrote, "This analysis details variations in menstrual cycle characteristics that are not widely known yet have significant implications for health and well-being."

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