You may already be familiar with the over-the-counter supplement melatonin, which has been around since the 1990s. But did you know that melatonin levels in ovarian follicles are three times higher than levels in blood? [1] How might naturally-occurring melatonin, which most people think of as a sleep aid, influence our fertility and health?
A brief review of what you already know about melatonin…
The hormone melatonin was originally identified in the pineal gland, which is located in the middle of the brain. But it’s also produced in the retina, skin, gastrointestinal tract, and reproductive organs [1]. Its most well-known purpose is to regulate the sleep-wake cycle, also known as the circadian rhythm. The circadian rhythm can be thought of as the body’s natural clock, a cycle of physical, mental, and behavioral changes that occur over a 24-hour day to maintain health. This is why melatonin supplements are used as a sleep aid for shift workers, people with insomnia, or travelers dealing with jet lag [2,3].
…plus what you probably didn’t know
In addition, melatonin is a free-radical scavenger and antioxidant. Free radicals are molecules with unpaired electrons that are produced as by-products of normal reactions in the body. Too many free radicals cause oxidative stress. Oxidative stress can damage healthy cells by destroying DNA, breaking apart cell membranes, and accelerating cell death. Antioxidants bind to free radicals to prevent this damage, acting like a molecular shield. Because of melatonin’s protective role in the body, ongoing research is looking into melatonin to help manage cancer, immunological disorders, diabetes, and viral infections [1].
Here, we will look specifically at melatonin and the work it performs to ensure a healthy cycle and maintain fertility.
Melatonin and the ovary
A brief overview of the female menstrual cycle can be found here. To summarize, ovulation is the primary goal of each menstrual cycle. Healthy, regular ovulation requires a series of coordinated events directed by hormones. Under the influence of follicle stimulating hormone (FSH), a few follicles are recruited and grow each cycle, producing estrogen until one follicle becomes dominant. Elevated estrogen causes a surge in luteinizing hormone (LH) from the brain, which triggers ovulation–the release of a mature egg from the dominant follicle. The follicle collapses and forms the corpus luteum, which produces the progesterone needed to maintain a pregnancy, should conception and implantation occur [4].
In a mature follicle, the oocyte, or egg, is surrounded by cells and follicular fluid. These cells perform the work needed for a successful ovulation [4]. The follicular fluid is made up of water, electrolytes, proteins, and hormones produced by the surrounding cells. It also has high concentrations of melatonin [1].
Melatonin’s role before ovulation
Preparing for ovulation requires a lot of cellular activity, and a rupturing follicle is an inflammatory event that generates free radicals. It is critical for the egg to be protected from oxidative damage, as poor egg quality can render conception difficult or impossible. This is perhaps why the follicle has such high concentrations of the powerful antioxidant melatonin. In other words, melatonin can shield the vulnerable egg from cellular damage naturally produced by the ovulation process [1,5,6].
Melatonin’s role after ovulation
Melatonin has a role to play after ovulation as well, working to prevent luteal-phase defects that can lead to infertility or early miscarriage. It helps the ruptured follicle form into the corpus luteum, and aids in progesterone production [5,6].
Problems with too little melatonin
It should come as no surprise, then, that low levels of melatonin are associated with smaller, immature follicles, lower levels of estrogen and progesterone, and poor egg quality.
[L]ow levels of melatonin are associated with smaller, immature follicles, lower levels of estrogen and progesterone, and poor egg quality.
For women with polycystic ovary syndrome (PCOS), reduced melatonin may be responsible for anovulation [1,7].
Other ways melatonin influences reproductive health
Both endometriosis and PCOS cause oxidative stress. Recall that melatonin protects against cellular damage caused by oxidative stress. A 2013 study found that supplementation helped mediate the inflammation and dysmenorrhea (painful periods) caused by endometriosis [8]. In another study, PCOS was induced in rats by reducing melatonin production [1]. Supplementation helped normalize cycles and hormone levels in women with PCOS. It also improved insulin sensitivity [2,9]. While more studies are needed, this early research into melatonin’s effects on various reproductive disorders looks promising.
Melatonin in pregnancy and in men
During pregnancy, melatonin also protects the developing fetus from oxidative stress. It is likewise important for placental development, and aids the placenta in producing human chorionic gonadotropin (hCG) [6,9]. While the developing fetus produces some melatonin, the sleep-wake cycle is still determined by the mother’s melatonin levels. Interestingly, low melatonin production has been observed in women with preeclampsia [2].
It should be no surprise that melatonin is important for male fertility as well. Melatonin protects the testes from local inflammation, and enhances the ability of Sertoli cells to respond to FSH [10]. Infertile men have higher levels of oxidative damage and lower levels of melatonin in their seminal fluid [3].
How can you support natural melatonin production?
Melatonin can be found in many foods, including:
- Eggs
- Fish
- Milk and kefir
- Nuts
- Fruits like tart cherries and strawberries
- Vegetables like tomatoes and peppers
- Cereals like wheat, barley, and oats
- Sprouted seeds [11,12]
Above all, quality sleep is critical. An estimated one-third of the world population suffers from sleep disorders. Melatonin production is halted by light exposure, which is why avoiding artificial light during the night is so important. One study demonstrated that two hours of tablet and smartphone use in the evening reduced melatonin production by 22%. Night shift work is known to disrupt reproductive cycles [2,6, 9, 11,12].
The bottom line
In darkness, during the quiet of the night, your body is working to produce a powerful hormone and antioxidant. Free radicals are products of normal life processes and are not bad in themselves, but can damage healthy cells if unchecked by antioxidants. Melatonin is necessary for fertility, both protecting cells in the reproductive tract from damage and allowing them to perform their work. By consuming nutrient-rich, whole foods and getting quality sleep, you can support melatonin production–and healthy fertility in the process. In other words, the work done in the night has an impact on every aspect of a healthy life.
