Table 1.

Environmental factors in neurodegenerative diseases.

Environmental Factors	Effects	Diseases	Reference
Heavy metals	Lead (crosses the blood–brain barrier and accumulates in neuronal and glial cells)	ALS 1	[3,4]
	Aluminium	AD 2	[5,6]
	Manganese	PD 3	[6,7]
Pesticide	Pentachlorobenzene	ALS	[8]
	Rotenone and paraquat	ALS, PD	[9,10]
	Organophosphate pesticides	ALS, PD, AD	[11]
Electromagnetic fields	Contradictory results	ALS, AD	[12,13,14]
Smoking	Protective	PD	[15,16]
	Risk factor	AD, ALS	[17,18]
Physical activity	Protective	PD	[19]
Body mass index and nutritional state	Lower nutritional parameters	AD	[20]
Microbiota structure and dysfunction of the gut–brain axis	Akkermansia muciniphila reduces symptoms; Ruminococcus torques and Parabacteroides distasonis	ALS	[21,22]
	Suppression of Prevotellaceae and anti-inflammatory genera; blooming of pro-inflammatory Proteobacteria, Enterococcaceae, and Enterobacteriaceae	PD	[23,24,25]
	Suppression of anti-inflammatory taxa such as Eubacterium rectale and a profusion of pro-inflammatory taxa such as Escherichia and Shigella	AD	[24,26]
Cyanobacteria and cyanotoxins	Risk factors	ALS, PD, AD	[27,28]

¹ ALS, Amyotrophic Lateral Sclerosis, ² AD, Alzheimer’s Disease, ³ PD, Parkinson’s Disease.