People with type 2 diabetes don’t respond properly to insulin, a hormone that controls the levels of sugar in their blood. Many of them have to take tablets to keep their sugar levels down, while others rely on insulin injections. But in a Swiss laboratory, there are diabetic mice with a more convenient solution. If they need more insulin, all they need is to bathe under a blue light.

The mice are the work of Haifeng Ye from ETH Zurich, who has developed a way of turning on individual genes with bursts of light. Blue light in particular sets of a chemical chain reaction in the rodents’ bodies that eventually switches on a gene called GLP-1. It tells the pancreas