Are you afraid of the dark? Diabetes is scary too

2 minute read

Night at light can bite.

Burning the midnight oil? Try not to burn your cardiometabolic health away with it.

There’s been a steady drumbeat of science warning that circadian rhythms are important and that knocking them sideways is a bad idea.

Light exposure at night does just this, disrupting the central circadian pacemaker in the hypothalamus, which sets the timetable for the processes required for glucose homeostasis.

Now a large study by an international team, including researchers from Monash and Flinders, seems to confirm that personal light exposure at the wrong time of day directly and independently increases your risk of type 2 diabetes, in a dose-dependent way.

When we say large study, we mean 85,000 UK Biobank participants, 13 million hours of data from wrist-worn light sensors and around eight years of followup.

Incident type 2 diabetes was measured, along with polygenic risk scores and a tonne of physical, lifestyle and sociodemographic covariates.

Using as a reference those in the bottom half for light exposure between half-past midnight and 6am, the team found incident diabetes risk was up 33% for those in the 50th to 70th percentile for light exposure; 44% for the 70th-90th; and 67% for the 90th-100th band, adjusting for age, sex and ethnicity.  

When the associations were additionally adjusted for income, material deprivation, education, and employment status, the hazard ratios for the same bands were 28%, 42% and 60%. When they were adjusted further for metabolic risk factors, smoking status, alcohol consumption, healthy diet, physical activity, urbanicity and, importantly, sleep duration and chronotype, it was 29%, 39% and 53%.

Light at night remained a significant predictor after shift workers were excluded. There were no significant sex differences.

Polygenic risk scores were a stronger predictor of diabetes. For comparison, the increase in risk between the reference group and the group with the most light exposure was around the same as the differences between adjacent quartiles of polygenic risk.

But they were entirely independent predictors. This means that, while most of the focus on modifiable risk factors goes on physical activity and weight loss, the genetically susceptible can lower their overall risk by keeping their environment dark at night.

Because the real monster under the bed is poor glycaemic control.

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