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Table 1 Characteristics of studies and salt intake estimates based on 24-h and overnight/spot urine samples

From: Change in mean salt intake over time using 24-h urine versus overnight and spot urine samples: a systematic review and meta-analysis

First author, Year, Country Mean age or range Female (%) Type of diet Length of follow-up and type of sample Equations used SALT INTAKE ESTIMATES
Data point 24-h urine Overnight/spot urine
N Mean salt intake, g/day N Mean salt intake, g/day
Studies that collected 24-h urine and overnight urine samples
Watson,1970 [25]
United States
21–23 years 100 Usual diet 1 year; Matched sample None; rate reported per hour 1 (B)a 25 5.96 ± 2.06 25 4.10 ± 1.64
2 (Y1) 25 6.89 ± 2.46 25 5.58 ± 3.63
Luft, 1982 [26]
United States
19–54 years 40 Controlled diet; meals in a clinical research center 15 days; Matched sample None; rate reported per 8 h 1 (B) 43 7.89 ± 1.53 43 5.26 ± 2.30
2 (D15) 43 8.12 ± 1.15 43 4.91 ± 1.15
Luft, 1982 [15]
United States
19–32 years 0 Controlled diet; meals in a clinical research center 7 days; Matched sample None; rate reported per 8 h 1 (B) 24 9.81 ± 6.30 24 5.24 ± 3.52
2 (D2) 24 9.58 ± 4.01 24 5.59 ± 3.09
3 (D3) 24 10.40 ± 2.58 24 5.61 ± 3.01
4 (D4) 24 10.92 ± 2.58 24 5.43 ± 2.15
5 (D5) 24 10.69 ± 2.86 24 5.63 ± 2.23
6 (D6) 24 10.22 ± 2.86 24 5.19 ± 2.32
7 (D7) 24 9.70 ± 2.58 24 5.26 ± 2.66
Liu, 1986 [16]
China
30–50 years 0 Usual diet 3 months; Matched sample None; rate reported per 12 h 1 (B) 49 13.51 ± 5.25 19 12.28 ± 7.12
2 (NS) 49 14.58 ± 5.44 19 12.86 ± 7.24
3 (NS) 49 15.34 ± 5.65 19 12.43 ± 5.34
4 (NS) 49 13.82 ± 5.70 19 10.97 ± 5.11
5 (NS) 49 14.81 ± 6.22 19 12.56 ± 7.08
6 (M3) 49 13.81 ± 5.59 19 11.72 ± 6.20
Liu, 1987 [17]
China
27–50 years
Mean: 35
0 Usual diet 10 days; Matched sample None; rate reported per 12 h 1 (B) 50 13.75 ± 5.71 50 13.27 ± 5.94
2 (NS) 50 15.14 ± 5.71 50 13.82 ± 5.54
3 (NS) 50 15.14 ± 6.48 50 14.27 ± 6.24
4 (NS) 50 14.28 ± 5.19 50 12.76 ± 5.92
5 (NS) 50 15.18 ± 6.48 50 13.81 ± 6.38
6 (D10) 50 14.97 ± 4.91 50 13.80 ± 5.75
He, 1993 [18]
China
19–55 years
Mean: 37
0 Usual diet 3 days; Matched sample None; rate reported per 8 h 1 (B) 63 8.58 ± 4.14 63 6.68 ± 4.01
2 (D2) 63 9.08 ± 4.91 63 7.24 ± 4.89
3 (D3) 63 9.65 ± 3.91 63 7.62 ± 4.36
Yasutake, 2015 [31], Japan Mean: 22 55 Controlled diet 15 days; Matched sample None; self-monitoring device used 1 (B) 10 8.60 ± 1.20 20 8.29 ± 0.98
2 (D15) 12 4.40 ± 1.30 20 6.63 ± 1.44
Yasutake, 2016 [19], Japan 20–70 years
Mean: 40
80 Usual diet Varies: 2 weekdays and 1 holiday; Matched sample None; self-monitoring device used 1 (B) 44 8.00 ± 1.80 50 8.00 ± 1.70
2 (NS) 44 8.50 ± 2.60 50 8.10 ± 1.80
3 (NS) 39 8.30 ± 3.30 50 8.30 ± 2.00
Kramers, 2019 [21], Netherlands 18–70 years
Mean: 46
52 Usual diet 6 weeks; Matched sample None; rate reported per 8 h 1 (B) 27 9.29 ± 3.27 27 8.41 ± 3.79
2 (W3) 27 8.70 ± 3.10 27 8.55 ± 3.51
3 (W6) 27 8.88 ± 3.91 27 7.57 ± 4.49
Studies that collected 24-h urine and spot urine samples
Do, 2016 [22]
Viet Nam
25–64 years
Mean: 45
53 Usual diet before and after an intervention 1 year; Unmatched sample 5 equations used; Intersalt treated as the main analysis 1 (B) 88 9.43 ± 3.69 509 8.48 ± 2.13
2 (Y1) 73 7.44 ± 4.09 511 8.05 ± 2.11
Petersen, 2016 [11], Australia 18 years and up 56 Usual diet 3 years; Unmatched sample (with some matched) 6 equations used; Kawasaki provided the closest estimate of the change 1 (B) 1000 8.37 ± 3.43 1000 11.69 ± 3.45
2 (Y3) 1012 7.89 ± 3.66 1012 11.27 ± 3.52
Huang, 2018 [23]
China
60 years and up
Mean: 66
50 Usual diet before and after an intervention Varies: up to 24 months
Unmatched sample (with some matched)
8 equations used; using individual volume spot provided the closest estimate of the change 1 (B) 532 10.92 ± 4.57 532 12.19 ± 7.37
2 (Y2) 2864 9.91 ± 4.32 2864 10.67 ± 6.60
Dong, 2018 [24]
China
10–15 years
Mean: 12
48 Usual diet 2–3 weeks; Matched sample 8 equations used; Whitton provided the closest estimate of the change 1 (B) 284 6.56 ± 2.69 284 9.92 ± 2.50
2 (W3) 284 7.26 ± 2.91 284 10.17 ± 2.48
Kim, 2018 [20]
South Korea
19–75 years
Mean: 50
49 Usual diet 16 weeks; Matched sample with two treatment groups 5 equations used; Intersalt provided the closest estimate of the change for both groups consistently 1 (B) 228 9.00 ± 4.07 228 7.41 ± 2.21
2 (M2) 228 9.15 ± 4.12 228 7.61 ± 2.35
3A (M4) 118 8.48 ± 3.51 118 7.62 ± 2.16
3B (M4) 111 7.12 ± 3.48 111 7.03 ± 2.19
  1. a B baseline; D day; W week; M month; Y year; NS not specified