Is Too Much Light Making Us Sick, Sad and Stressed?
Many of us may not be getting enough melatonin at night.
Posted Jan 02, 2018
As we dim the lights in the evening and start winding down for the night, the pineal gland in our brains starts to release the hormone melatonin.
Our nightly dose of melatonin plays a fundamental role in keeping us healthy. It keeps oxidative stress in check and undue inflammation at bay. It coordinates our body clock, modulates insulin function and acts on cholesterol pathways. It helps to seal the walls of the intestines, preventing endotoxin-related inflammation, and also secures the blood brain barrier.
Overnight darkness is critical to our well-being because the pineal gland can only produce melatonin if it is dark enough, but technology, globalisation and shift work are blurring the lines between night and day, and shrinking the amount of darkness we're exposed to overnight.
As a result, many of us are not producing enough melatonin.
Melatonin lowered inflammation, insulin resistance and BP in diabetic patients.
In a recent double blind, randomised, controlled trial on a group of patients with type 2 diabetes and coronary heart disease (30 patients and 30 age-matched healthy controls) taking 10mg of melatonin tablets an hour before bedtime every night for three months significantly reduced markers of inflammation (high sensitivity C-Reactive Protein) and insulin resistance (HOMA-IR), improved cholesterol parameters (increased HDL and decreased LDL and serum triglyceride levels) and even lowered blood pressure.
Just because a treats b does not imply b was caused by an absence of a, but taken in light of accumulating evidence, the findings of the study raise the possibility that an absence of melatonin may, at least in part, have contributed to the patients' illness.
Can a deficit in melatonin be partly to blame for the global rise in metabolic disorders?
Through working late, looking at blue screens all night and staying indoors all day, urban life in the developed world is shrinking our usual daily dose of melatonin. In parallel, obesity, type 2 diabetes and hypertension are all on the rise.
We know that rodents given a "junk" food diet during their awake hours put on less weight than their friends eating the same diet erratically throughout the day. A study on mice has also shown how melatonin mitigates the memory impairment caused by eating a high fat diet.
Could disordered melatonin dynamics be contributing to the rise in obesity and type 2 diabetes in the industrialised world by exacerbating the negative effects of a highly processed, refined food diet?
Melatonin acts in the "Goldilocks" zone.
Melatonin, like other cogs in the wheel of human physiology, acts in an optimal golden zone which applies to both dosage and timing. It may not always be a deficiency per se of melatonin that causes problems, but its inappropriate timing.
The dose must be just right, at just the right time. Too much or too little are equally harmful. The evening onset of melatonin is important, but so is the morning offset.
As an example, melatonin in the evening makes us insulin-resistant whereas in the morning, melatonin hampers the release of insulin in response to a rise in blood sugar. Too much melatonin in the morning (e.g. through supplements) may impair blood sugar regulation and invite metabolic disorders.
A delayed offset of melatonin in the morning (such as from heading to bed late and sleeping in late) has been linked to depression, while a delayed onset of melatonin (leading to less melatonin overnight) may worsen mania.
Melatonin and stress.
Melatonin and stress have an intricate relationship. Melatonin influences the autonomic nervous system, acting against stress, while stress raises resting sympathetic tone, which interferes with melatonin production at night.
Insufficient melatonin at night, in turn, raises sympathetic tone during the day. This increases emotional arousal as we go about our day, so we get stressed over small things.
Stress (and the inflammation it triggers) promotes tryptophan metabolism along the kynurenine (rather than the serotonin) pathway, as cortisol and inflammatory agents IFN-gamma and IL-6 promote the enzymes TDO, IDO and KMO respectively. This affects serotonin dynamics, and in turn, melatonin dynamics.
The kynurenine pathway metabolites can encourage inflammation within the brain and may cause havoc in the gut, which melatonin and serotonin pathways are not able to act against.
This can have far-flung effects on hunger, obesity, metabolism, mood and intestinal permeability.
Is your brain missing the sunset?
When our ancestors first discovered fire, they mastered two elements of their environment, light and heat.
Candlelight resembled the last light of a sunset and when electricity came along, we lit our evenings with the warm, red-spectrum hues of incandescent light, reminiscent of a brighter, intense sunset.
Today, the interval between day and night is erratic, abrupt and lacks a sunset of any kind as LED lights perpetuate the bright blue light of daytime. The only way to give our brains a sunset in the middle of our urban jungles is to artificially create one.
A sunset follows a day of sunshine, so try to get as much daylight as possible during the day. This increases melatonin production at night. In the evening, make your lighting as red and dim as possible. Many electronic devices now offer blue light filters and blue blocking glasses are becoming increasingly available. Heat, food, noise and exercise also act against melatonin, so they’re better if shifted to earlier on in the day.
I asked for some blue-light blocking glasses this Christmas and my resolution for 2018 is to give my brain the gift of a sunset every evening this year.
Raygan F, Ostadmohammadi V, Bahmani F, Reiter RJ, Asemi Z. Melatonin administration lowers biomarkers of oxidative stress and cardio-metabolic risk in type 2 diabetic patients with coronary heart disease: A randomized, double-blind, placebo-controlled trial. Clin Nutr. 2017 Dec 12.
Alzoubi KH, Mayyas FA, Mahafzah R, Khabour OF. Melatonin prevents memory impairment induced by high-fat diet: Role of oxidative stress. Behav Brain Res. 2018 Jan 15;336:93-98.
Rubio-Sastre P, Scheer FA, Gómez-Abellán P, Madrid JA, Garaulet M. Acute melatonin administration in humans impairs glucose tolerance in both the morning and evening. Sleep. 2014 Oct 1;37(10):1715-9.
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Muller MD, Sauder CL, Ray CA. Melatonin attenuates the skin sympathetic nerve response to mental stress. Am J Physiol Heart Circ Physiol. 2013 Nov 1;305(9):H1382-6.
O'Farrell K, Harkin A. Stress-related regulation of the kynurenine pathway: Relevance to neuropsychiatric and degenerative disorders. Neuropharmacology. 2017 Jan;112(Pt B):307-323.