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Table 1 Examples of environmental factors and their biologic correlates

From: The interplay of aging, genetics and environmental factors in the pathogenesis of Parkinson’s disease

Protective factors Biologic correlates
Smoking • Nicotine acts at nicotinic acetylcholine receptors to trigger downstream effects that reduce neuronal damage [30]
Physical activity • Increases serum urate [31]
• Increases neurotrophic factors [32]
Urate • Anti-oxidant by activating of Nrf2/antioxidant response pathway [33]
Ibuprofen • Anti-inflammatory effect by activation of peroxisome proliferator-activated receptor gamma (PPARγ) [34]
Calcium channel blockers • Plausible blockage of calcium-channel induced metabolic stress of mitochondria of DA neurons [35]
Caffeine • Adenosine A2A receptor blockade [36]
Risk factors
 Pesticides • Mitochondrial toxins, oxidative stress [27, 28]
 Dairy • Urate-lowering effects of dairy products [37]
 Traumatic brain injury • Breakdown of blood-brain barrier, brain inflammation, impaired mitochondrial function, increase in glutamate release, α-synuclein accumulation [38]
 Anxiety or depression • May be prodromal symptom rather than risk factor due to loss of serotonergic neuronal cells in dorsal raphe nucleus in early PD [39]
 Beta-blockers • Aggravate the loss of norepinephrine neurons in locus coeruleus and deficits in norepinephrine in PD [40]