New Scientist – Suzanne De la Monte has interfered with the way the rats’ brains respond to insulin and produces results that mimic dementia. The hormone is most famous for controlling blood sugar levels, but it also plays a key role in brain signalling. When de la Monte disrupted its path to the rats’ neurons, the result was dementia.
Poor sensitivity to insulin is typically associated with type 2 diabetes, in which liver, fat and muscle cells fail to respond to the hormone. But results such as de la Monte’s have led some researchers to wonder whether Alzheimer’s may sometimes be another version of diabetes – one that hits the brain. Some have even renamed it “type 3 diabetes”.
If they are right – and a growing body of evidence suggests they might be – the implications are deeply troubling. Since calorific foods are known to impair our body’s response to insulin, we may be unwittingly poisoning our brains every time we chow down on burgers and fries. People with type 2 diabetes, who have already developed insulin resistance, may be particularly at risk. “The epidemic of type 2 diabetes, if it continues on its current trajectory, is likely to be followed by an epidemic of dementia,” says Ewan McNay of the University at Albany in New York. “That’s going to be a huge challenge to the medical and care systems.”
* 115 million people globally will get Alzheimer’s by 2050
* 5.4 million adults in the US have Alzheimer’s now. The US care cost was $130 billion in 2011 alone.
* Worldwide, 36 million people have the Alzheimer’s now
All of which highlights the importance of eating healthier foods and taking exercise to reduce your risk of dementia. It may even be possible to reverse – or at least decelerate – some of the cognitive decline in people who already have Alzheimer’s, by targeting the underlying insulin resistance. If so, that would suggest new treatments for the disease, which has so far evaded any attempt to treat it.
Weight gain seems to amplify the problem – 80 per cent of people with type 2 diabetes are also overweight or obese. Though the mechanism is still unclear, obesity seems to trigger the release of inflammatory and metabolic stress molecules inside liver and fat cells that disrupt insulin action, leading to high blood glucose levels and, eventually, insulin resistance.
If McNay and de la Monte are correct, a similar process may lead to Alzheimer’s. They think that constantly high levels of insulin, triggered by the fat and sugar content of the western diet, might begin to overwhelm the brain, which can’t constantly be on high alert. Either alongside the other changes associated with type 2 diabetes, or separately, the brain may then begin to turn down its insulin signalling, impairing your ability to think and form memories before leading to permanent neural damage. “I believe it starts with insulin resistance,” says de la Monte. “If you can avoid brain diabetes you’ll be fine. But once it gets going you are going to need to attack on multiple fronts.”
For the time being, there are measures that everyone can take to help stave off cognitive decline. Since insulin resistance emerges from a bad diet, laying off fatty and sweet foods might help to reduce the risk of developing Alzheimer’s. Conversely, diets rich in certain kinds of fatty acids might help the brain to maintain good insulin signalling. Exercise, too, can encourage the body to conquer insulin resistance – which may explain why regular physical activity reduces your risk of Alzheimer’s by 40 per cent.