In the village of Agincourt in South Africa, every family receives a little money from the state. A pension or a child grant, about 21 dollars a month. It is like a stream that flows into every home. Scientists wanted to find out whether this stream affects blood sugar, because diabetes is very common in places like this.
For seven years they followed 4580 adults. They measured blood sugar at the start and at the end. And they found: if a family receives 100 rand more a month, the risk of prediabetes drops by 6%. Prediabetes is when blood sugar is already above normal but not yet diabetes. The payments, however, have no effect on diabetes itself.
The stream does not put out a fire, but it keeps it from flaring up. If diabetes has already begun, money will not replace pills. But if blood sugar has only just started to rise, regular help can stop it. It is like watering a garden a little every day: the lake will not fill up, but the plants will survive. Until now no one knew that payments could work this way. Now it is clear: even small money, if it comes regularly, helps people stay healthy.
The highest glucose level recorded in the study was 30.6 mmol/L, which is three times the diabetes threshold and life-threatening. Yet the average payment per person was only about 21 dollars a month, less than the cost of a single doctor's visit in developed countries.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.