Anyone considering using Viagra as a treatment for impotence could be forgiven for thinking there is now another reason to go ahead with it. Some say that this class of drugs, known as PDE5 inhibitors, may protect people from developing Alzheimer’s disease.
It sounds like a medical news story that is too good to be true – and sadly, in this case, the headlines are probably premature.
The stories are based on a study that found taking drugs for erectile dysfunction is linked with a lower risk of Alzheimer’s. at University College London and her colleagues looked at anonymised medical records of nearly 270,000 men in the UK aged 40 or older who had a new impotence diagnosis.
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Those who went on to get prescriptions for Viagra (sildenafil) or a similar drug had an 18 per cent lower chance of being diagnosed with Alzheimer’s over the next five years.
It isn’t implausible that this class of drug could protect against dementia. These therapies are being investigated for several medical conditions, including helping protect babies from oxygen deprivation during childbirth, and Viagra was originally developed as a treatment for heart disease.
The drugs work by raising levels of a chemical signalling molecule called cGMP that dilates blood vessels and so boosts blood flow to the penis. Animal research has shown that these drugs also dilate blood vessels to the brain, which could keep it in better shape.
A second potential mechanism is that they raise levels of a nerve signalling molecule called acetylcholine, which could help brain cells communicate with each other better. Indeed, some existing medicines that slightly alleviate dementia symptoms work by boosting acetylcholine.
But we need to be careful about drawing conclusions from this kind of study. The best form of medical evidence comes from randomised trials, where, for instance, hundreds of men would be given either Viagra or placebo pills and their subsequent rates of Alzheimer’s compared.
The new findings come from the other main kind of research: an “observational” study, where scientists just use records to observe different patterns of behaviour, such as using Viagra or not, to see if that correlates with different health outcomes.
Observational studies are easier to do than randomised trials, but are prone to bias because a third factor could be linked with Viagra use and be protective against Alzheimer’s disease. It is why scientists often say “correlation doesn’t prove causation”.
Bauer and her team adjusted their results for several possible confounding factors, including age and many health aspects. But it is generally impossible to adjust for every confounding factor. In this case, for instance, they couldn’t take account of the men’s physical activity levels, as this wasn’t listed in their medical records.
It is plausible that men who sought prescriptions for impotence pills were also more motivated to stay physically active and it was this that protected them from Alzheimer’s. Keeping fit is one of several lifestyle measures advised for reducing your risk of dementia. “We know that activity protects against Alzheimer’s disease,” says Bauer.
The latest results aren’t, therefore, a reason to see erectile dysfunction drugs as a silver bullet for preventing dementia, with the added bonus of treating erectile dysfunction. They may, however, be a stimulus for carrying out randomised trials in the hope this will provide firmer evidence. “Our study can’t say for sure it’s the drugs that are responsible for the protective effect,” says Bauer. “More research is definitely needed.”
Neurology
