There's a reasonable amount of published literature on this type of thing. For example in the case of Parkinsons https://news.nationalgeographic.com/2018/01/sm

There's a reasonable amount of published literature on this type of thing. For example in the case of Parkinsons https://news.nationalgeographic.com/2018/01/smell-sickness-parkinsons-disease-health-science/ https://news.nationalgeographic.com/2018/01/smell-sickness-p...