In the past week there have been three very important peer reviewed studies released about light in relation to health. I wanted to write a brief report summarising these amazing studies so we can continue our learning together about light, health and our circadian rhythms.
Blue Light disrupts the circadian rhythm and create damage in skin cells.
In 2017 a study emerged that showed a photo-transmitter called melanopsin was discovered in human fat cells. This was important as it showed that our fat cells are circadian and can be controlled by light. The industry then hypothesised that blue light could therefore also impact the skin but no meaningful study had come out to support these claims. That was until now.
The skin has two important functions, during the day it is focused on protection while at night it focuses on repairing damage that occurred during the daytime and preparing the skin for the next morning.
Our circadian rhythms provide the precise timing cues for this to happen and are fundamental in keeping our skin healthy. Our skin has its own indepenant circadian rhythms. We know light and dark cycles are the biggest stimulus for circadian entrainment. It was very exciting when this study showed that our skin can change its circadian function by being exposed to blue light (specifically at 410nm) after dark.
It was shown that skin cells can sense light directly and control their own clock gene expression. This means if you are wearing your BLUblox blue light glasses after dark but exposing your skin to blue light, your skin will think is still daytime. I always talk about fixing your light environment, so you have complete protection against blue light as blue light blocking glasses are only one weapon in our arsenals in the fight against blue light after dark.
If our skin cells think its daytime at night-time they will not function in a way that stimulates repair of skin damage sustained during the day. This means increased reactive oxygen species production, DNA damage and inflammation. This could be why we are seeing an increase in skin cancers across the world as the circadian rhythms of the skin are seldom in a state of repair and DNA damage could lead to skin cancers. Let’s not blame UV light for what artificial blue light after dark may be doing to our skin.
Human milk as “chrononutrition”: implications for child health and development
It is very clear to all of us that have had children or even know someone who has children, that sleepless nights are very common and often seen as a standard entry into parenthood. However, a new study is now suggesting that the development of circadian rhythms in babies could be tied to mother’s breast milk.
We know that fixing the lighting environment we live in is better for maintaining circadian entrainment in adult humans but the same is true for babies. For example, having red lights in the baby's sleeping quarters for night feeds, total black out rooms for sleep and minimising blue light exposure after sunset are all essential. However, in babies it seems circadian rhythms of set by the mother’s breast milk.
This study has shown that human breast milk can be called “chrononutrition”, meaning that human milk communicates time of the day information to babies. The issue, in the USA for example, is that 85% of breast-fed babies are fed pre-pumped breast milk from their mothers and not directly from the breast.
Milk made during the day in mothers was highest in cortisol. Cortisol is a hormone that is released during the day in humans and advises our circadian clock that its day time and makes us feel alert. Milk created in the breast after sunset was devoid of cortisol and high in tryptophan and melatonin, two hormones when secreted that make us feel relaxed and sleepy and advise our brain its night time.
If a breastfeeding mother pre-pumps her breast milk and gives her baby milk pumped during the day, after sunset, this will administer high levels of cortisol to the infant and tell the developing brain that its daytime and to be awake rather than relax for sleep. He same is true if the mother gives milk pumped after sunset to their baby during the day. The baby will feel sleepy during the day when they should be more alert and awake.
This is vitally important for a baby’s development as dysregulated circadian biology may compromise infant health and development.
The hack to mitigate this is to label pre-pumped breast milk and to ideally avoid formula milk substitutes as they will not contain the correct hormones for your baby.
Endogenous circadian regulation of female reproductive hormones.
If you are a woman reading this blog, you will know that getting pregnant “doesn’t just happen” and most of the time it takes a few tries to conceive. What if we told you this could be down to your circadian rhythms?
It appears this could be the case. In this new study it has been shown that female reproductive hormones exhibit 24-hour rhythms with specific hormones being released at specific times. A disrupted circadian rhythm could mean more difficulty getting pregnant, something that seems to have become more prevalent in recent years.
The female reproductive hormones are also under “endogenous circadian regulation, defined as persisting in the absence of external time cues. These results may have important implications for the effects of circadian disruption on reproductive function.”
This study is well worth reading should you wish to be starting a family soon or starting to go through a change in hormones such as menopause or have irregular period cycles.
It is fascinating that when I study the new research that emerges weekly on circadian rhythms that almost every process in humans is controlled by them. It seems that our food contains hormones that regulate circadian functions, that some circadian rhythms are governed by internally processes whereas others are from external cues.
What is very clear is that we need to be protecting not just our eyes after dark from blue and green light from 400-550nm but also our skin. I would therefore like to reiterate that after sunset your lights in your house are red, your digital devices are switched off or blue light filters applied and to have either black out curtains or a 100% black our sleep mask whilst you sleep. This along with wearing blue light blocking glasses are the staples of good light hygiene.
If you have a baby ensure the above practise are adhered to along with giving them breast milk pumped at the correct time of the day, label your bottles with a date and time stamp.
I will continue to provide updates on the latest research when it arises in a clear and basic way so we can all add to our knowledge of how light and circadian rhythms impact our health, wellness, ageing and sleep. Studies will always be listed below should you like to dive deeper into the technical details.