Recovering the Biological Clock with Light

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It’s no secret that as we age, the reproductive potential of women decreases – the fertility cycle becomes more irregular the closer we get to menopause, in all female mammals including humans.  Some new research is shedding light (literally) on how light-dark cycles (think the sun and moon phases in each 24-hour period) may be a major driver of these changes.


Many of the body processes follow a natural daily rhythm called a circadian rhythm.  It’s based on the day and night cycle of a 24 hour period.  Many hormones are produced only in certain hours of the circadian clock (like melatonin production at night time in a dark room), the detoxification processes shift throughout the day, and even body temperature is altered depending on time of day.  Circadian rhythms are regulated by small regions of the brain called the suprachiasmatic nuclei (SCN).  These nuclei act as control centers, connected to other parts of the brain, and follow a regular cyclical patter of activity that repeats itself every 24 hours.


There is a direct pathway that runs from the eyes to the SCN, and light exposure plays the largest role in setting your circadian clock.  Basically, exposure to sunlight sets the time clock and keeps your body in this natural rhythm on a daily basis. 


In a healthy person, circadian rhythms cycle easily and naturally, orchestrating a vast array of physiological processes.  There are many links in the literature to alteration of circadian rhythms with disease processes – like breast cancer risk in women who do shift work. 


Some new literature is emerging that shows these light-dark cycles, or circadian rhythms, may also affect fertility.


Researchers set out to determine if there was a link between altered circadian rhythms and reproductive potential in this new study.  They divided female mice into two groups, young females (2-6 months) and middle-aged females (8-12 months), and evaluated how regular their cycles were under various light-dark conditions.  What they found was that altering the light-dark exposure conditions in young mice didn’t significantly alter their fertile cycles.  In contrast, middle-aged mice showed marked differences between fertile activity rhythms when their light-dark cycles were altered on a weekly basis.  82% of these mice, in fact, exhibited normal fertile cycles under normal light-dark conditions and irregularity under the weekly shifted schedule.  Perhaps even more exciting is that, if these mice with irregular cycles were then exposed to the normal 24-hour light-dark cycle, regular fertile cycles were recovered.


In basic terms – this study showed that older female mice are very sensitive to light and dark cycles (more so than younger mice).  Altering the hours of the day that older female mice were exposed to light started to change their fertile cycles.  And changing the exposure back to normal returned their regular cycles.


In mice, at least, age-related reproductive dysfunction (irregular cycles) can be reversed by changing the environmental timing signals. 


In humans, this may mean that the effects of jet lag, shift work, use of blue screens at inappropriate times (computers before bed) and improper sleep schedules have an impact on the fertility of women as they age.  Researchers concluded, “there may well be an association between contemporary irregular lifestyles and irregular menstrual cycles in humans.” 


Here are some of our basic recommendations to preserve your circadian clock:

-no blue light exposure (cell phones, tablets, computers, or TV watching) in the hour before going to bed

-be in bed, sleeping, in complete darkness, by 10pm

-ensure your bedroom is free of any ambient light, use blackout curtains and unplug anything with a light; or use an eye mask

-get, at minimum, 7 hours of deep sleep each evening, ideally starting at 10pm

-consider using a light alarm, instead of a sound alarm, to gently bring yourself out of the sleep rhythm in the morning

-consider changing work schedules if yours requires shift work


While more research must be done on the effects of light-dark cycles on human fertility, this new literature is exciting.  We are always harping on our patients to get proper sleep, and try not to use computers/phones/tablets before going to bed – and here’s a bit of research to back up why that may be extremely important for female fertility, especially as women age.


Kali MacIsaac HBSc, ND
Naturopathic Doctor




Recovering the biological clock with light -, Fertility and Reproductive Natural Medicine