Bright light exposure has a profound effect on regulating the circadian system in humans. Dr. Panda and colleagues discovered that melanopsin — a light-sensitive protein found in specialized cells of the eye — responds to blue light and synchronizes the body's day/night cycle. Melanopsin-containing cells detect blue light from the sun but also from electronic devices. In response to the amount of blue light, melanopsin signals the brain to produce or repress melatonin production, a hormone that induces sleep. Therefore, dimming lights and avoiding devices in the evening allows melatonin to rise naturally. Conversely, morning bright light exposure suppresses already-declining melatonin levels, improving alertness and resetting the circadian clock. In this clip, Dr. Satchin Panda explains how light exposure affects the circadian clock and how dimming lights and avoiding devices in the evening allows melatonin to rise naturally.
Rhonda: You brought up a lot of really important points for one talking about avoiding bright lights or blue light exposure in the evenings. And, some people may not be familiar with why that is. So a key driver of the body's circadian rhythms is melatonin, which, people probably have heard of it's a sleepiness hormone, but, it rises towards the evening because blue light, inhibits it.
So can you talk a little bit. about Maybe that, and perhaps even the opposite of avoiding bright light in the evening would be actually seeking it out in the morning.
Satchin: Yeah. So, this, discovery of, melanopsin of the blue light receptor was considered to be one of the top 10 breakthroughs of the year in 2001, when three different labs, including mine, we discovered it, to give you a context, if you're living in the nature, and you don't have access to electrical lighting.
then the day length changes between summer and winter. And accordingly, our sleep and wake up time also has to change our circadian rhythm has to adjust to this changing daylight. So as a result, our nature has...we have evolved to have this light sensor, this specialized type of light sensors. These are called melanopsin or blue light sensing, light sensors that are present in our retina.
These are not necessarily for seeing the outside world, but this light sensor senses blue light and why blue light? Because the sunlight is the best source of blue light. When we say blue, it's around 450 nanometer to 500 nanometer that range. So these light sensors in our retina, they actually are slightly different because they need, a good dose of blue light.
When I say good dose, that means for example, in a full moon night, your regular light sensors can help you find their way, or you can take a walk. but that level of light is not enough to activate melanopsin. So that means if you stay awake and you are taking a night hike in a full moon night, it's not going to reset your circadian clock. and Now fast forward few years, what we understand now is this melanopsin blue light sensor actually senses light bright light. during the daytime or blue light from electrical lighting and then tells our master circadian clock in the brain depending on what time it is and might say, Hey, it may not be evening.
It's actually extension of the day. It's a long summer day, so please stay awake. Or at the same time, it can also send a signal to this melatonin, which is the sleep hormone because when melatonin goes up, we tend to feel sleepy. It tells melatonin that, Hey, it's not time to go up because it's just a long summer day.
So that's the way this blue light sensor in our retina connects to our brain to reset our clock or to tell when melatonin should rise or fall. So now. What are the functional consequences or how we can use this information in everyday life? one is since, melatonin has to rise a melatonin rise correlates very well with, how we, feel sleepy and how we fall asleep.
It's a good idea to let it rise naturally so that we can fall asleep and to let it rise. Naturally, we have to release the brake and the brake here is blue light. And that's why dimming down light in the evening is a good idea to release that brake so that melatonin can begin to rise. And since we know that this is blue light as the cause of suppressing melatonin, we can also do another thing.
We can change the color of the light and based on this science, almost all the cell phones. or Laptops now have a night shift or night light feature and you can program it to turn it on around 8:00 or 9:00 in the evening when these screens will dim down and will turn it orange in color They may or may not help you to increase your melatonin, but at least they will, signal that it's time to wind down and go to bed.
Then conversely, during daytime, it's very important to get a good dose of bright daylight. so that means if you are sitting next to a window, a large window and having your breakfast, although you don't have sunlight falling on your eyes, you still get around 1000 lux of daylight. And if you have that exposure for half an hour to an hour in the morning, then that's pretty good enough.
to Again, put a strong brake on melatonin, which might be slowly going down in the morning. And at the same time that melanopsin receptor, it does slightly different things. During daytime. It sends a signal to the brain to increase alertness and make us more functional. So it reduces depression and makes us more happy.
So that way we can use this information that we learn from a very fundamental discovery in neuroscience to our advantage by getting at least 30 to 60 minutes of daylight, even sitting next to a large window during the first half of the day and dimming down light and maybe switching to yellow or orange-shifted light or wearing even blue filtering eyeglasses in the evening to improve our sleep.
Rhonda:So a couple of questions, one, You mentioned avoiding the blue...sorry, wearing the blue filtering glasses at night, perhaps to filter out some of the blue light. What about avoiding sunglasses early in the day to make sure you're activating the melanopsin receptor and getting that resetting of the circadian clock?
Satchin: Yes, that's a good question, because we also have to strike the balance between protecting our eyes and getting enough blue light.
so let's talk about some actual numbers of how much light we experience. So if you are outside in a sunny day in California or sunny day in any place, and if you're looking at the sky, not looking at the sun, you get somewhere between 100,000 to 200,000 Lux of light. so very simple calculation.
And if you're inside your car, And there is no direct sunlight falling on your face or inside your car. And you're just driving, looking horizontally, Then, you're getting somewhere between 5,000 to 10,000 lux of light, which is similar to standing outside your car in a cloudy day, that's also 5,000 to 10,000 lux of light. So now in a cloudy day or sitting inside your car, there is not enough UV light to hit your eye and damage your cornea or damage your skin. So in that case, driving without sunglasses is fine because you are not getting too much UV light exposure, but if you are in the beach or you are outdoors skiing in a very sunny day, and you have a lot of UV exposure, then it may not be a good idea to abandon your sunglasses.
Rhonda:Interesting because the, singlet oxygen produced by blue light can damage. the rods and cones.
Satchin:There is a ton of UV light outside too.
Rhonda:And what about, on the flip side of that, people actually being exposed to the bright light in the evening, oftentimes think, well, I can take a melatonin supplement and that should sort of help me increase my melatonin.
A wavelength of light emitted from natural and electronic sources. Blue light exposure is associated with improved attention span, reaction time, and mood. However, exposure to blue light outside the normal daytime hours may suppress melatonin secretion, impairing sleep patterns. In addition, blue light contributes to digital eye strain and may increase risk of developing macular degeneration.
The body’s 24-hour cycles of biological, hormonal, and behavioral patterns. Circadian rhythms modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, metabolism, and others, ultimately influencing body weight, performance, and susceptibility to disease. As much as 80 percent of gene expression in mammals is under circadian control, including genes in the brain, liver, and muscle. Consequently, circadian rhythmicity may have profound implications for human healthspan.
A gene encoding a transcription factor (CLOCK) that affects both the persistence and period of circadian rhythms. CLOCK functions as an essential activator of downstream elements in the pathway critical to the generation of circadian rhythms. In humans, polymorphisms in the CLOCK gene have been associated with increased insomnia, weight loss difficulty, and recurrence of major depressive episodes in patients with bipolar disorder.
A mood disorder characterized by profound sadness, fatigue, altered sleep and appetite, as well as feelings of guilt or low self-worth. Depression is often accompanied by perturbations in metabolic, hormonal, and immune function. A critical element in the pathophysiology of depression is inflammation. As a result, elevated biomarkers of inflammation, including the proinflammatory cytokines interleukin-6 and tumor necrosis factor-alpha, are commonly observed in depressed people. Although selective serotonin reuptake inhibitors and cognitive behavioral therapy typically form the first line of treatment for people who have depression, several non-pharmacological adjunct therapies have demonstrated effectiveness in modulating depressive symptoms, including exercise, dietary modification (especially interventions that capitalize on circadian rhythms), meditation, sauna use, and light therapy, among others.
An essential mineral present in many foods. Iron participates in many physiological functions and is a critical component of hemoglobin. Iron deficiency can cause anemia, fatigue, shortness of breath, and heart arrhythmias.
A measure of the intensity of light. One lux is equal to the illumination of a one-meter square surface that is one meter away from a single candle. The lux intensity of sunlight far exceeds that of typical artificial lighting.
An opsin-like protein, sensitive to light with a peak sensitivity around 480 nm, and found in the very small proportion of retinal ganglion cells which are photosensitive. It is believed to be the visual pigment that synchronizes the circadian cycle to the day-night cycle as well as being involved in the control of pupil size and the release of melatonin.
A hormone that regulates the sleep-wake cycle in mammals. Melatonin is produced in the pineal gland of the brain and is involved in the expression of more than 500 genes. The greatest influence on melatonin secretion is light: Generally, melatonin levels are low during the day and high during the night. Interestingly, melatonin levels are elevated in blind people, potentially contributing to their decreased cancer risk.
A chemical that causes Parkinson's disease-like symptoms. MPTP undergoes enzymatic modification in the brain to form MPP+, a neurotoxic compound that interrupts the electron transport system of dopaminergic neurons. MPTP is chemically related to rotenone and paraquat, pesticides that can produce parkinsonian features in animals.
A type of reactive oxygen species. Singlet oxygen is generated in cells as a result of exposure to UV light or visible irradiation. It induces damage in cellular proteins, keratinocytes (a type of skin cell), and DNA.
The highest level of intake of a given nutrient likely to pose no adverse health effects for nearly all healthy people. As intake increases above the upper intake level, the risk of adverse effects increases.
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