Table 2.
Quality of overall evidence for each environmental factor
| Factor | N Studiesa | Overall Strength Of Evidenceb | Direction Of Associationc | ||
|---|---|---|---|---|---|
| C | X | R | |||
| Air | |||||
| Nitrogen oxides (NOx) | 2 | Strong | ↑ | ||
| Carbon monoxide (CO) | 1 | Moderate | ↑ | ||
| Environmental tobacco smoke | 1 | Moderate | ↑ | ||
| Particulate matter (PM10&2.5) | 1 | 1 | Strong | ↑ | |
| Ozone (O3) | 1 | 1 | Strong | ↑ | |
| Toxic heavy metals | |||||
| Arsenic | 2 | Moderate | ↕ | ||
| Lead | 1 | Weak | ↑ | ||
| Other metals | |||||
| Aluminium | 1 | 15 | Moderate | ↕ | |
| Calcium | 1 | Weak | – | ||
| Cobalt | 1 | Weak | – | ||
| Copper | 2 | 1 | Weak | ↕ | |
| Iron | 2 | 1 | Weak | ↕ | |
| Manganese | 1 | Weak | ↑ | ||
| Molybdenum | 1 | Weak | – | ||
| Nickel | 1 | Weak | – | ||
| Uranium | 1 | Weak | – | ||
| Zinc | 2 | Weak | ↕ | ||
| Other trace elements | |||||
| Fluoride | 1 | Weak | ↑ | ||
| Selenium | 1 | Moderate | ↕ | ||
| Silicon (and silica) | 2 | 2 | Strong | ↕ | |
| Occupational | |||||
| Aluminium (occupational exposure) |
1 | 3 | Weak | ↕ | |
| Defoliants/fumigants | 1 | Weak | ↑ | ||
| Diesel motor exhaust | 1 | Moderate | – | ||
| Electromagnetic fields | 1 | Moderate | ↕ | ||
| Excessive noise | 1 | Weak | ↓ | ||
| Glues/adhesives | 1 | 1 | Weak | ↕ | |
| Pesticides/fertilizers/herbicides/insecticides | 5 | 2 | 2 | Strong | ↕ |
| Lead (occupational exposure) | 1 | Weak | – | ||
| Metals (occupational exposure) | 1 | Moderate | ↑ | ||
| Inks/dyes | 1 | Weak | – | ||
| Paints/stains/varnishes | 1 | Weak | – | ||
| Gasoline/fuels/oils | 1 | Weak | – | ||
| Solvents/degreasers | 2 | 1 | 1 | Strong | ↕ |
| Liquid plastics/rubbers | 1 | Weak | – | ||
| Vibratory tools | 1 | Weak | – | ||
| Radiation | 1 | Weak | ↑ | ||
| Miscellaneous | |||||
| Climate | 1 | Weak | – | ||
| Electric and magnetic fields | 1 | 2 | Moderate | ↕ | |
| Mobile phone use | 1 | Weak | ↓ | ||
| Vitamin D | 3 | 1 | Strong | ↑ | |
| Water pH | 1 | Weak | ↑ | ||
a C cohort studies, X cross-sectional studies, R reviews. Studies can appear in multiple rows
bStrength of evidence is assessed according to the criteria outlined in Table 1
cIncreased levels of the exposure are associated with: ↑ an increased risk of dementia; ↓ a decreased risk of dementia; ↕ mixed results on dementia risk; and – no substantial effect on dementia risk