Why would sunlight improve diabetes?

In October of last year, Italian police raided a ‘Ndrangheta mafia strong house in Reggio Calabria, Italy. As expected, they found a hoard of cannabis. But a less expected find was a freezer full of mice . Apparently, the mafia had a tradition of serving plump mice at special feasts of reconciliation between warring factions.

This type of mice, called dormice, was very popular in the Roman times. The Romans would fatten them up in special jars, by feeding them chestnuts and keeping them in the dark to make them believe it was time to get ready for hibernation.

I bring this story up because it's germane to one of the scourges of modern life: diabetes.

Type 2 diabetes is a curious disease. In my opinion and in the opinion of some scientists (and this is a minority view, not the mainstream orthodox view), it's not a disease caused by failure of an organ or tissue. It's a disease where the body becomes mis-programmed and executes a series of metabolic changes that is supposed to be used in a different circumstance. Your body is doing something it's programmed to do, but at the wrong time.

The changes that happen in diabetes - higher levels of sugar in the blood, increase in fat stores, etc. are all changes that happen in animals when they (and we) get ready for winter. In some species (such as bears and squirrels that hibernate), these changes are pronounced - their glucose, cholesterol, and weight all increase dramatically as they approach winter. In humans, they are usually less pronounced, but we also store up fat for winter.

Type 2 diabetes is an exaggerated, wrongly-timed version of what naturally happens. Something tells your body "winter is coming, get ready for it." (Type 1 diabetes is something altogether different.)

What causes this? It's not clear. Some people think it's the fructose in our diet. Fructose is normally never seen by our bodies except during fall, when fruits ripen. And certainly it is not normally seen in the quantities many of us consume. In studies, you can trigger insulin resistance (the first step toward diabetes) by giving healthy volunteers just a few cans of fructose-containing soft drink for just a few weeks. So drinking fructose-containing soda or eating fructose-enhanced food may signal to the body that winter it coming. (Fructose also wreaks havoc on the liver and increases body weight so it's just bad all-around.)

Another intriguing possibility, though, is exposure to sunlight. Most organisms use the length of day to sense the change of seasons. And most organisms are biologically programmed to respond to changes in seasons - by changing their habits, metabolism, fur, etc.

In fact, if a scientist didn't know about Type 2 diabetes, and someone asked her how we might make people gain weight, increase cholesterol, and increase blood sugar levels, one idea that she might come up with might be: make the body think it's wintertime by reducing the length of sunlight exposure per day.

In modern society, many of us spend more time indoors than outdoors. This might make it hard for our bodies to track seasons.

Or, alternatively, we use a lot of artificial light, including blue light-emitting computer screens. This may confuse our seasonal clocks and may make it difficult for our bodies to tell whether the days are getting longer or shorter, and whether winter is coming or not. And our bodies may just default to the safe choice, which is to store up fat for the winter (and one of the best way to store up fat is for our cells to ignore insulin signaling, and become diabetic).

This hypothesis is supported by data. In one study of over 10,000 subjects, increased exposure to sunlight had a statistically significant beneficial impact on blood glucose levels (sunlight also lowered cholesterol levels, as would be expected). To be clear, the cause of diabetes is probably multi-factorial, but this study's results make sense, since the amount of sunlight probably has a significant effect on your body's seasonal clock.

Of course, more sunlight may make people more active, which may have a beneficial effect on diabetes. But, recall that the Romans used to keep dormice in the dark to make them think it's wintertime, which made the mice fatter (and probably also threw them into diabetic state).

This sunlight hypothesis is not widely studied, partly because most scientists believe that diabetes is a failure of our body, rather than a legitimate program that is mis-triggered. (This is, I believe, the same mistake some aging researchers make when they see aging as deterioration of our body rather than a programmed process.)

Interestingly, one of the best medicines for diabetes is bromocriptine. By best, I mean the one with very impressive effect on survival (many drugs that lower glucose actually worsen survival, which is why the FDA now requires pharma companies to prove their drug doesn't increase mortality before the drug will be approved). One of the hypothesis about how bromocriptine works is that it resets the seasonal clock in our bodies, and pulls us out of the winter-preparation mode.

As I said, this is a minority view, that Type 2 diabetes is a problem of mis-signaling. But as a biologist, I tend to think that our bodies, after billions of years of evolution, is a pretty well-functioning machine. It's rare that it breaks down in the absence of injury or pathogens. I think it's more likely that there is something in our modern life that is sending a wrong signal to our bodies, and diabetes is probably a normally a beneficial program that is being executed at the wrong time.