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Table 2 Quality of overall evidence for each environmental factor

From: Environmental risk factors for dementia: a systematic review

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

  1. aC cohort studies, X cross-sectional studies, R reviews. Studies can appear in multiple rows
  2. bStrength of evidence is assessed according to the criteria outlined in Table 1
  3. 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