Some expert opinions on the article https://www.sciencemediacentre.org/expert-reaction-to-study-...
> Sildenafil is more often prescribed to wealthy people and low socioeconomic status is associated with higher risk of Alzheimer’s.
> There are other possible explanations for these findings; for example, we know that brain changes start decades before dementia symptoms and it is possible that these early Alzheimer’s changes reduce sex drive (thus people wouldn’t ask for a prescription for erectile dysfunction). [...] They did try to control for this by looking into patients with pulmonary hypertension, which is sometimes treated with sildenafil. However, this group did not have a statistically significant decreased risk in Alzheimer’s disease.
> people who take sildenafil have less serious cardiovascular damage than those who are taking the other drugs to combat hypertension or diabetes. If cardiovascular damage is a key causal factor in developing Alzheimer’s disease, then these people might anyway be at an advantage compared to people who have to take drugs for hypertension, cardiovascular disease or diabetes. The study tried to control for this, but it is not clear if severity of the different conditions controlled for could be taken into account (those with more severe hypertension are presumably more likely to be taking anti-hypertensive medication such as losartan).
Many of the opinions are quite positive though, and praise the high sophistication of the statistical methods.