Many of us sit by a window to boost our mood, but exposure to natural light during the day also seems to improve blood sugar control in people with type 2 diabetes.

Our cells and tissues follow circadian rhythms, 24-hour cycles of metabolic activity that regulate things like blood sugar levels. Studies have shown that exposure to artificial light at night disrupts these rhythms, , while spending more time outside in sunlight seems to , a hormone that helps keep these levels in check.

But none of these studies explored the potential benefits of being exposed to natural light through a window, even though most people spend the vast majority of their time indoors, says at Maastricht University in the Netherlands.

To learn more, Hoeks and his colleagues recruited 13 people with type 2 diabetes with an average age of 70, who spent 4.5 days in a room where they were solely exposed to natural light, through large windows, between 8am and 5pm.

The participants, who continued to take their usual diabetes medications, mainly sat at a desk where they had access to their phones and computers, with these screens set to a low level of brightness. In the evenings, they were exposed to dim artificial light and had access to their devices until 11pm, before sleeping in complete darkness until 7am. They all ate three similar meals a day, designed not to make them gain or lose weight, and did the same exercises at fixed points across the 4.5 days.

The researchers also carried out a very similar experiment with the same participants, but this time they sat in windowless rooms with only artificial lighting. This was done either a month before or a month after the natural-light part of the study.

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During both experiments, the participants wore devices that continuously monitored their blood sugar levels, although technical problems meant this data was only available for 10 of them.

This revealed that, during the natural-light week, the participants’ blood sugar levels remained within a healthy range 50 per cent of the time. In the artificial light experiment, this range was only achieved 43 per cent of time.

Definitions of a healthy blood sugar range vary. The researchers defined it as between 4.4 to 7.2 millimoles per litre, which is more or less in line with what the and the say.

Although the data differences may seem relatively small between the two experiments, spending a lot of time outside of a healthy range could make a difference to someone’s , such as heart problems, says Hoeks.

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As to why sunlight exposure may have this effect, light-sensitive cells in the eye are central to regulating cycles of metabolic activity and are more sensitive to the shorter wavelengths found in natural light, says Hoeks.

Further studies are needed to establish this, he says, but for now, many people with type 2 diabetes could benefit from getting more natural light, even if that means just sitting by a window. “It’s easy, accessible at no cost and available to everyone,” says Hoeks. It is unclear whether people with type 1 diabetes or prediabetes – when someone’s blood sugars are higher than usual, but not high enough for a type 2 diabetes diagnosis – would benefit to the same extent.

at University College London says that larger studies are needed to confirm the findings. Nevertheless, he adds that “the importance of daylight is only slowly beginning to be appreciated”.

The hepatitis B vaccine seems to reduce the risk of developing diabetes, and not just by preventing the infection.

The vaccine is routinely offered to infants in most countries, usually via three doses. In the US, this became part of the vaccination programme in 1991, so only .

Scientists have previously found . This may be due to the hepatitis B virus – which infects the liver and spreads through blood, semen and vaginal fluids – from the blood. This could raise the risk of diabetes, where blood sugar levels are persistently too high.

But prior studies have not looked at whether the vaccine might reduce diabetes risk among a group of both immunised and non-immunised people who haven’t contracted hepatitis B, which would suggest the effect acts independently of just preventing the infection.

To explore this, at Taipei Medical University in Taiwan and her colleagues analysed the health records of more than 580,000 people living across the US, Europe, Africa, Latin America, the Middle East and the Asia-Pacific. On average, these records spanned nearly four years for each individual between 2005 and 2023.

None of the participants, who were aged between 18 and 90, had any kind of diabetes or had been infected with the hepatitis B virus, according to their records and the absence of infection-specific blood markers. About half of them had received a hepatitis B vaccine, gauged according to levels of virus-specific antibodies in their blood.

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The team found the vaccinated participants had an overall 15 per cent lower rate of diabetes – defined as them either receiving a diagnosis, having a persistently high blood sugar level or being prescribed diabetes drugs – than their unvaccinated counterparts. The vast majority of cases were type 2 diabetes, the most common form of the condition. The results will be presented at the European Association for the Study of Diabetes Annual Meeting in Vienna, Austria.

Although this is observational research, the scientists also found a dose-response effect, where the vaccinated participants with higher levels of hepatitis B-specific antibodies were less likely to develop diabetes than those with lower levels. Differences in antibody levels may be a reflection of how many vaccine doses the individual participants received, how recently they were immunised or general variation in immune responses.

As to the mechanism, the fact none of the participants had knowingly been infected with hepatitis suggests being immunised reduces diabetes risk independent of just preventing infection, says Phan. One potential explanation is it somehow reduces chronic inflammation that damages the liver and pancreas, which release hormones that regulate blood sugar levels, like insulin, she says.

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However, the scientists can’t rule out the possibility that part of the vaccine’s protective effect comes from preventing the infection, she says. They hope to explore the potential pathways involved, and how they may vary between different forms of diabetes, in studies in mice, says Phan.

It is possible people who get vaccinated are simply more likely to make lifestyle choices that reduce type 2 diabetes risk, such as eating a healthy diet and exercising regularly. “People who are prone to get vaccinated are generally people who are more conscious about living a healthy life,” says at the University of Veterinary Medicine Hannover in Germany.

The team accounted for factors that could affect the results, such as the participants’ age, sex and whether they smoked or had other conditions, like obesity and high blood pressure. But Osterhaus maintains the influence of such factors cannot be ruled out.

Drugs like Ozempic and Wegovy, called GLP-1 agonists, carry more benefits than risks when taken for their approved uses, according to a comprehensive analysis of their effects on 175 conditions. The same may not be true for people taking the drugs for other uses, however.

“In this new land of GLP-1, we wanted to really map the benefits and risks for all conditions that might be plausibly linked,” says at Washington University in Saint Louis, Missouri.

The drugs are best known for helping people control type 2 diabetes and treat obesity. They mimic a hormone in the body, GLP-1, that lowers blood sugar levels and makes people feel fuller for longer.

Dozens of studies suggest GLP-1 agonists may also cut the risk of a slew of other conditions, from heart disease to dementia to substance use disorders. These studies have involved hundreds or thousands of people and focused on just one or a few conditions at a time, but millions of people are now using the drugs, meaning we can investigate less frequent effects, says Al-Aly.

To gain a more comprehensive picture, he and his colleagues examined the health records of more than 200,000 people with diabetes who took GLP-1 agonists in addition to their standard treatment over a four-year period. They also looked at 1.2 million people with diabetes who only received standard care across the same period, and assessed the risks of both groups developing 175 different health conditions.

The team found that those who took GLP-1 agonists had a lower risk of 42 conditions. For instance, their risk of heart attacks was reduced by 9 per cent and their risk of dementia dropped by 8 per cent. The odds of this group having suicidal thoughts or substance use disorders, including addiction to alcohol and opioids, also decreased by around a tenth – even when the team accounted for factors that could affect the results, such as participants’ age, sex and income levels.

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There were downsides for the people taking GLP-1 drugs, however. They were more likely to experience known side effects including nausea and vomiting, along with others not described before. These include a 15 per cent higher risk of kidney stones and more than double the risk of an inflamed pancreas, or drug-induced pancreatitis. In total, risks were higher for 19 conditions, while for most of the conditions assessed, including bronchitis, rheumatoid arthritis and obsessive-compulsive disorder, taking GLP-1 drugs had no meaningful impact on risk levels.

The fact that these drugs do affect such a wide range of conditions is still surprising, although exactly why they have this impact is unclear. “They’re reducing obesity, which is sort of the mother of all ills – you treat it and subsequently get benefit in the heart, the kidney, the brain and everywhere else,” says Al-Aly. They also generally dampen organ-damaging inflammation and seem to target parts of the brain related to addiction, he says.

One issue with the analysis is that the team didn’t report the actual number of people affected by each condition, making it hard to interpret the results, says at the University of Toronto, who has worked with obesity-drug companies. While the risk reductions in common conditions like heart attacks and dementia are probably worth taking seriously, he says, the links to rarer conditions like pancreatitis might involve a very small number of cases and so pose little risk to most people. Al-Aly says the team will be presenting specific case numbers in a future study.

Overall, the research provides reassurance that the benefits of GLP-1 agonists outweigh the risks, at least for people with type 2 diabetes and obesity. “There are no red flags for this group,” says at University College London, who has also worked with an obesity-drug firm.

But for those without these conditions, such as people without obesity buying the drugs to lose weight, the picture may differ. “We have no idea if the benefits will outweigh the risks,” says Drucker.