Comment la lumière du matin peut influencer vos efforts de perte de poids
De: https://articles.mercola.com/sites/articles/archive/2024/06/25/morning-light-weight-loss.aspx
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How Bright Morning Light Can Influence Your Weight Loss Efforts
Story at-a-glance
- Syncing your circadian rhythm through morning bright light therapy can potentially help you lose weight, according to research
- In one study, a group of participants who were asked to get an hour a day of bright morning light lost more body fat after undergoing an exercise program, compared to the group who received indoor lighting
- Your circadian rhythm affects numerous biological processes, one of which is your sleep-wake cycle. Hormone secretion, cellular function and gene expression all rely on your circadian rhythm, so once it is thrown off, then all these processes are severely affected
- To reap the benefits of sunlight for better sleep, I recommend getting bright daylight first thing in the morning for at least 10 to 15 minutes. This will stop melatonin production and signal your body that it's time to wake up
If you need a good reason to go out and spend more time in the sun, here’s something that may help convince you — getting enough sunlight during daytime could potentially help you lose weight.
An article published in NutritionFacts.org1 explores this potential benefit, and explains the driving factor for this effect is your circadian rhythm.2 Dr. Michael Greger, the author of the article, posits, "If weakening our circadian rhythm can cause weight gain, might strengthening it facilitate weight loss?"
The Circadian Rhythm’s Role in Your Health
Before we go deeper into this topic, let’s quickly review what the circadian rhythm is. Basically, circadian rhythms act as internal clocks in your body. According to the Sleep Foundation:3
"Circadian rhythms [are] the natural patterns that take place in your body over the course of each 24-hour cycle. [They] are controlled by biological clocks located in organs and glands throughout the body, but all of these peripheral clocks are commanded by a ‘master clock’ in a region of the brain called the suprachiasmatic nucleus."
In most adults and adolescents, the circadian rhythm operates on a cycle that is slightly longer than 24 hours. However, it relies on external stimuli to help entrain this rhythm daily, and the two most powerful stimuli are light and darkness.
Your circadian rhythm affects numerous biological processes, one of which is your sleep-wake cycle. Based on signals of light and darkness, your brain’s suprachiasmatic nucleus (SCN) tells your pineal gland when it's time to secrete melatonin — promoting sleep — and when to turn it off.
Hormone secretion, cellular function and gene expression all rely on your circadian rhythm, so once it’s thrown off, all these processes are severely affected. Today, the two primary culprits that affect your circadian rhythm are exposure to light at night and insufficient exposure to natural light during the day.
Lulu Guo, a Sleep Medicine physician, says, "Changing the amount and times of sunlight exposure, or changing our routines, can send signals to our ‘master clock’ and shift our natural circadian rhythms."4
Exposure to light leads to advances or delays in your circadian rhythm, known as phase shifts. Typically, exposure to light early in the morning causes a phase advance, which leads to earlier waking. Light exposure at bedtime will lead to a phase delay, or later wakening.
Exposure to Light at Night Can Cause Weight Gain
Since the beginning of time, humans have been exposed to light from sunlight during the day and near complete darkness at night. Once the sun sets, early humans only relied on light from the moon, stars and fire.
Today, it’s difficult for most people to avoid light exposure at night, as we have televisions, computers and cellphones within arm’s reach, along with light pollution and the advent of LED bulbs. While these do offer convenience in some cases, excessive exposure can cause a cascade of health problems, including diabetes, heart disease and obesity.
In the featured article,5 Greger highlights how a weakening circadian rhythm due to inappropriate light exposure can lead to a higher risk of obesity. He refers to a 2016 study,6 which used wrist meters to take note of the participants’ ambient light exposure. The researchers discovered that a heightened exposure to light at night was correlated with a subsequent increased risk of developing obesity over time.
And if some would think that insufficient sleep is to blame and not light exposure, Greger quotes another study,7,8 this time involving more than 100,000 women. It found that, independent of the participants’ sleep duration, higher nighttime light exposure still led to an increased risk of obesity.
"You can’t know for sure if nocturnal light exposure is harmful in and of itself until you put it to the test. When that was done, those randomized to exposure to bright light for a few hours in the evenings or exposed even just for a single night suffered adverse metabolic consequences," he said.
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Download PDFGetting Bright Light in the Daytime Can Help With Weight Loss
Greger then raises another intriguing question — Can syncing your circadian rhythm through morning bright light therapy potentially help you lose weight? Studies — some even dating back to the 1990s9 — say it can.
In 2007, the first randomized controlled trial10,11 regarding daytime light exposure and obesity was published. Participants were divided between those who were asked to get an hour a day of bright morning light and those who only received normal indoor lighting. All of them were then asked to undergo an exercise program. The researchers found that the group who received bright morning light lost more body fat than the indoor lighting group.
"[T]he findings of this study indicate that the temporal pattern of light exposure during the daytime can influence body weight independent of sleep timing and duration …
[L]ight is a powerful biological signal and appropriate timing, intensity and duration of exposure may represent a potentially modifiable risk factor for the prevention and management of obesity in modern societies," they concluded.12
Another study13 involving female participants notes that even getting bright light in advance can boost performance and stimulate weight loss. The participants were divided into two groups; one group was exposed to dim light and the other was exposed to bright light during the daytime.
The following day, both groups were asked to do a handgrip endurance test. The researchers noted that the bright light group’s mean number of contractions was 864.5, while the dim light group was 766.63.
"Regardless of the mechanism, bright morning daylight exposure could present a novel weight-loss strategy straight out of the clear blue sky," Greger said.14
Getting Proper Sun Exposure Is a Cornerstone of Optimal Health
As the studies mentioned above highlight, optimal sun exposure in the daytime can help adjust your body’s internal clocks and sleep-wake cycles, allowing you to get high-quality sleep at night.
The near-infrared light you get from sunlight also activates cytochrome c oxidase (CCO), which in turn enhances the production of melatonin in your mitochondria. There’s actually an intimate link between sunlight and melatonin. In fact, there are two types of melatonin — circulatory, which is produced by your pineal gland and secreted in the blood, and subcellular, which is made in your mitochondria where it is locally used.
However, both types are connected and controlled by either the absence or presence of sunlight. If you fail to expose your skin to sufficient near-infrared light from the sun, then your mitochondria will have seriously depleted melatonin levels that can’t be corrected through supplementation.
For you to reap the benefits of sunlight for better sleep, I recommend getting plenty of bright sunlight exposure in the morning and at solar noon. Exposure to bright light first thing in the morning for at least 10 to 15 minutes, stops melatonin production and signals your body that it's time to wake up.
While you can simply open your window and let the sun’s rays in, going outdoors is better — you might even want to take a quick morning walk. Then, a few hours later, you can step outside again, around solar noon, to get more sun.
I highly recommend getting at least an hour of sensible sun exposure daily to reap optimal benefits, including optimizing your vitamin D production. This is why spending time outdoors is one of the cornerstones of optimal health, as it can have a profound impact on your mind and body.
Get Rid of Poor Nighttime Habits and Avoid Blue Light at Night
The U.S. Centers for Disease Control and Prevention (CDC)15 states that lack of sleep is now a public health epidemic, as it’s linked to a wide variety of health problems, including stroke and heart disease. It also affects your cognitive performance,16 triggers depression17 and even puts you at risk of accidents.18
Unhealthy nighttime habits, such as using your cellphone and/or tablet and watching TV before bedtime, are a significant contributing factor why many people are not getting enough sleep. These modern gadgets also emit blue light wavelengths, which have been linked to eye damage,19 obesity, diabetes and heart disease.20
I highly recommend adopting simple strategies to reduce your exposure to blue light, especially hours before bedtime. Once the sun has set, dim your lights and turn off your electronic devices. Ideally, keep these devices out of your bedroom.
Normally, your brain starts secreting melatonin between 9 p.m. and 10 p.m., and these devices emit light that may stifle that process. After sundown, shift to a low-wattage incandescent bulb with yellow, orange or red light if you need illumination. You can also use a salt lamp illuminated by a 5-watt bulb, as it will not interfere with your melatonin production.
If you need to use a computer or smartphone, I advise installing blue light-blocking software like Iris,21 which is an improved version of f.lux. However, an easier solution is to wear blue-blocking amber-colored glasses. I found an Uvex model (S1933X)22 on Amazon that costs less than $9 and works like a charm to eliminate virtually all blue light.
This way you don't have to worry about installing programs on all your devices or buying special light bulbs for evening use. Once you have your glasses on, it doesn't matter what light sources you have on in your house.
More Tips to Create a More Conducive Sleep Environment at Night
Sleeping in total darkness can be challenging, especially if you live in an urban area. Even if you eliminate all light sources in your bedroom, including your digital alarm clocks, the streetlights, city lights and headlights of cars passing by outside can still penetrate your sleeping chamber. One solution is to use blackout shades to keep lights out. For a less expensive alternative, simply wear a sleep mask when you go to sleep.
In areas of your home that you always frequent, I recommend installing incandescent bulbs, as these are less efficient at suppressing melatonin. Leave the LEDs for places like in closets, garage and porch, where you have minimal exposure to them.
For more tips to optimize your sleep, I recommend reading my article "Tips and Tricks to Help You Fall Asleep Faster." Applying these adjustments to your daily routine and bedtime habits can go a long way toward ensuring you get uninterrupted, restful sleep every night, allowing you to achieve better health.
Addressing This Can Help You Maintain a Healthy Weight Naturally
Aside from optimizing your sleep habits and getting enough sunlight during the day, making healthy changes to your diet is a significant factor in helping you lose excess weight. Remember that the primary factor driving the overweight and obesity epidemics today is the excessive amounts of linoleic acid (LA) in our diet.
LA is the most common omega-6 fat found in seed oils like canola, soybean, corn, sunflower, cottonseed and safflower. Reducing your intake of seed oils and all processed foods is a powerful way to support a healthy weight.
Ideally, consider cutting your LA intake down to below 5 grams, or better yet, 2 grams per day. This is close to what our ancestors used to get before chronic health conditions became widespread.
To do this, you will need to avoid all ultraprocessed foods, fast foods and restaurant foods, and to prepare your meals at home. For more information on the dangers of linoleic acid, I recommend reading my article, "Linoleic Acid — The Most Destructive Ingredient in Your Diet."
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