In the UK, heart failure affects over one million people, with around 170,000 new cases diagnosed yearly.
The condition, which occurs when the heart muscle can’t pump enough blood to meet the body’s needs for blood and oxygen, is often the result of damage from conditions such as heart attacks or uncontrolled high blood pressure.
If you’re keen to naturally lower your risk, well-researched advice centres around eating a heart-healthy diet, exercising regularly, avoiding cigarettes and alcohol, and keeping conditions like hypertension under control.
But beyond the obvious measures, scientists are now exploring the impact of another, far less obvious factor: light. Particularly, exposure to bright light while we sleep.
While switching off the lights has long been linked to deeper, more restful sleep, emerging evidence suggests bedding down in the pitch black could also deliver extra, unexpected benefits for our hearts.
What the research says about light and the heart
Having a light on at night can be comforting for safety if you’re scared of the dark, but there may be good reasons to rethink your nighttime set-up.
According to research published in JAMA Network Open, people who sleep in brightly lit rooms – such as those with an overhead bedroom light on – have a 56% greater risk of developing heart failure than those who sleep in total darkness.
In the largest study of its kind to date, researchers tracked nearly 89,000 adults aged 40 and over, using wrist-worn light sensors to measure the amount of artificial light they were exposed to at night. Alongside this, they looked at their individual health records from over nearly a decade.
The results showed that exposure to brighter light during sleep was associated with a significantly higher risk of multiple major cardiovascular conditions, even after accounting for age, lifestyle, sleep habits, and other established risk factors.
Alongside a higher risk of heart failure, those who slept under the most intense light also had a 32% higher risk of coronary artery disease and a 28% higher risk of stroke.
While the researchers were quick to caution that the study doesn’t definitely prove light causes heart disease, they did write that it shows a strong correlation, even when other lifestyle factors were taken into account.
Sleeping with a light on might carry risks for heart health, say experts.
(Andrii Lysenko via Getty Images)What scientists think is going on
The researchers don’t know why light at night may raise heart risk, but they reckon several biological mechanisms might be at play, based on existing research.
Firstly, viewing bright light at night interferes with your circadian rhythm, your body’s internal 24/7 clock that has a hand in your sleep, hormone regulation, blood pressure and metabolism. When your body clock is thrown slightly out of whack by a change in usual light levels, it can put strain on the cardiovascular system.
Similarly, darkness also triggers the release of melatonin, the sleep hormone that helps you to wind down before bed, but also regulates blood pressure and reduces inflammation, which are all key risk factors for cardiovascular disease.
In addition, the study authors write that previous lab studies underscore a link between a raised nighttime heart rate and bright lights, which prevent your blood pressure from naturally dipping during the night.
However, other experts say we should look at the research through a wider lens, as light exposure is unlikely to be acting on its own.
Emily McGrath, senior cardiac nurse at the British Heart Foundation says: “Previous research has found that light exposure at night can affect the body’s glucose metabolism, and that this is associated with a greater risk of obesity and heart disease.
“But people who are exposed to more light at night also tend to get less sleep, and a lack of sleep can increase the risk of cardiovascular disease, too.
“When sleep duration is taken into account, the link between light exposure at night and cardiovascular risk is reduced, as was seen in this study,” she notes.
“We need more research to better understand the impact of artificial light on our bodies, and to separate its effects from other night-time factors, such as shift work.”
Bright light can interfere with sleep, and a lack of quality kip can increase the risk of cardiovascular disease.
(zhihao via Getty Images)Tips for making sleep more heart-healthy
While the wearable devices measured personal light exposure at night, the researchers didn’t look at where the light was coming from – whether it was bedside lamps and hallway lights, screens and nightlights, or outdoor light pollution, such as streetlights filtering into bedrooms.
This means it’s difficult to quantify whether sleeping with a light on carries the same risk as being exposed to constant outdoor light pollution, such as living on a busy, well-lit street.
Still, if you’re keen to make your slumber a little less stressful on your heart, small changes could help. Here are a few ticker-friendly steps you could take:
Sleep in the dark
Before you bed down, switch off lamps, TVs and overhead lights, and consider blackout curtains if outside light creeps in.
Give your devices a hard bedtime
Phones and tablets emit a type of unique blue light, which is thought to inhibit the release of melatonin. To avoid confusing your body clock, try powering down at least an hour before sleep.
Keep a regular sleep routine
Aside from dimming the lights, going to bed and waking up at roughly the same time each day helps keep your body clock in sync.
Avoid spice and alcohol
When it comes to diet, spicy foods, alcohol and large meals can take a long time to digest, so these should be avoided in the hours before bedtime. Opt for lighter snacks and sleep-supporting herbal teas.