Table 1 Summary of the main features of retrieved studies

Studies research design

 Case–control

2

 Cohort

30

 Cross-sectional

41

 Ecological

28

Samples

 Cross-national population samples

16

 National population samples

66

 Regional/community samples

19

Geographical allocation of studies’ samples

 EU

61

 North America (USA and Canada)

18

 Australasia (Australia and New Zealand)

7

 Asia (China, Japan, South Korea)

6

 South America (Argentina and Brazil)

2

 Multicentre

7