Millions of Americans work night shifts in all industries, with up to 18 percent of workers enduring alternating night shift schedules. Several studies have linked shift work, and specifically working during the night, to menstrual disorders, miscarriage and preterm birth.
For many people, night shift work is a necessary part of their lifestyle. If this is the reality for you, it's worth understanding how this may affect your reproductive health, what to watch for and what you can do about it.
Disrupting the body's internal clock
"Our bodies follow circadian rhythms that respond primarily to light and dark. These light and dark cycles are important for the function of our brain—they regulate our body's internal clock," explained Kimberley Thornton, M.D., a reproductive endocrinologist and infertility specialist at Reproductive Medicine Associates of New York and an assistant professor at Icahn School of Medicine in New York City.
"When individuals go against the natural light and dark cycles by working at night and sleeping during the day, it can disrupt our circadian rhythms," Thornton said.
While digestive function can quickly adapt to a change in sleep schedules, the brain's internal clock is less amenable, leading to crossed signals.
"It is believed that this causes some biological signals in our body to say it's daytime while other signals are saying it is night, which leads to overall disruption of metabolism, which has been linked with health problems," Thornton continued.
Reproductive health can suffer
Night shift work is correlated to increased risk of irregular menstrual cycles, miscarriage and infertility, but the exact mechanisms for this negative impact on reproductive health are not well understood by scientists. However, there are some theories, including one about the impact on hormonal function.
"We believe that the shift in circadian rhythms may affect regulation of the reproductive hormones that control the menstrual cycle," Thornton said.
"Once there is a pattern of fluctuating circadian rhythms, the body is now unregulated in its timing and release of hormones necessary in regulating menstrual cycles, healthy pregnancies and term births," added Monica Grover, D.O., M.S., head gynecologist with VSpot, a New York City medical spa specializing in vaginal health.
'We believe that the shift in circadian rhythms may affect regulation of the reproductive hormones that control the menstrual cycle.'
When hormones become unregulated, the body cannot produce adequate concentrations of hormones or sustain their normal functioning. For women of reproductive age, this can lead to lower estrogen levels, inadequate gonadotropin release and an impaired luteinizing hormone (LH) surge, all of which can impair ovulation and conception.
"This can all result in a prolonged waiting time to pregnancy as well as sustained menstrual irregularities," Grover explained. "Studies have shown an increased risk of spontaneous abortion, preterm birth or intrauterine growth retardation if a woman is pregnant."
Stress hormones can also become unbalanced, which can affect reproductive health.
"Circadian rhythm misalignment can also increase cortisol levels and lead to further insulin resistance, leading to impaired ovulatory cycles," Grover said. "Increased cortisol levels are also considered part of a systemic inflammatory response, which may lead to a higher incidence of endometriosis."
"If a woman is working the night shift and experiencing these issues, it may be best to try and switch to the day shift," Thornton advised.
If you can't entirely eliminate night shift work, Grover suggests limiting the number of consecutive night shifts or trying to transition from quickly rotating shifts (every one to three days) to slowly rotating shifts, such as weekly.
For many women, though, this is not an option. In that case, the experts recommend optimizing other lifestyle modifications that you can control.
"Eat healthily, exercise regularly, avoid toxic substances, such as tobacco intake, and make sure to get enough sleep daily," Thornton advised. "By maximizing other areas of your health, you can help minimize impacts from working at night."
"It is also essential to be mindful during these work hours to take adequate rest breaks, if possible, for meals and naps, and [schedule] additional rest days," Grover added. "If there are prolonged days off or rotating days off, it is vital to maintain a consistent sleep pattern during the day."
If you are experiencing reproductive health issues, seeking medical care from a physician is essential.