Table 1 Baseline characteristics of the participants according to sex, categories of water intake, and hydration status

Median

900

900

900

400 ml/day

900 ml/day

1300 ml/day

1800 ml/day

292 mmol/L

298 mmol/L

304 mmol/L

Range

(0–3100)

(0–2700)

(0–3100)

(0–500)

(800–1000)

(1071–1400)

(1800–3100)

(263–294.9)

(295–299.9)

(300–346.5)

Frequency, n

1957

989

968

390

744

546

277

123

400

669

 Age (years)

65. 0± 4.9

66.2 ± 4.0

63.70 ± 5.36

< 0.001

65.0 ± 4.9

65.4 ± 4.8

64.9 ± 5.0

64.0 ± 4.7

< 0.001

64.2 ± 5.0

64.3 ± 5.0

65.2 ± 4.8

0.008

 Sex (women)

989 (50.5)

989 (50.5)

968 (49.5)

188 (48.2)

383 (51.5)

280 (51.3)

138 (49.8)

0.731

47 (38.2)

190 (47.5)

353 (52.8)

0.008

  Primary school

1023 (52.3)

629 (63.6)

394 (40.7)

188 (48.2)

399 (53.6)

297 (54.4)

139 (50.2)

68 (55.3)

211 (52.8)

372 (55.6)

  High school

545 (27.9)

235 (23.8)

310 (32.0)

111 (28.5)

201 (27.0)

148 (27.1)

85 (30.7)

29 (25.6)

112 (28.0)

184 (27.5)

  College

389 (19.9)

125 (12.6)

264 (27.3)

< 0.001

91 (23.3)

144 (19.4)

101 (18.5)

53 (19.1)

0.381

26 (21.1)

77 (19.3)

113 (16.9)

0.636

  Single, divorced or separated

242 (12.4)

136 (13.8)

106 (11.0)

47 (12.1)

96 (12.9)

62 (11.4)

37 (13.4)

17 (13.8)

46 (11.5)

77 (11.5)

  Married

1513 (77.3)

684 (69.2)

829 (85.6)

300 (76.9)

560 (75.3)

423 (79.1)

221 (79.8)

97 (78.9)

319 (79.8)

520 (77.7)

  Widower

202 (10.3)

169 (17.1)

33 (3.4)

< 0.001

43 (11.0)

88 (11.8)

52 (9.5)

19 (6.9)

0.311

9 (7.3)

35 (8.8)

72 (10.8)

0.645

 Body mass index, kg/m²

32.6 ± 3.5

33.0 ± 3.6

32.3 ± 3.4

< 0.001

32.3 ± 3.4

32.7 ± 3.5

32.5 ± 3.5

33.3 ± 3.5

0.001

32.3 ± 3.1

32.5 ± 3.4

32.8 ± 3.5

0.245

 Physical activity (MET min/day)

348.7 ± 334.4

284.0 ± 244.6

414.8 ± 395.5

< 0.001

330.5 ± 322.4

345.2 ± 335.4

364.1 ± 348.9

352.6 ± 325.6

0.502

423.9 ± 338.2

364.5 ± 337.9

344.2 ± 346.8

0.057

  Never smoked

904 (46.2)

704 (71.2)

200 (20.7)

182 (46.7)

334 (44.9)

263 (48.17)

125 (45.1)

47 (38.2)

175 (43.8)

333 (49.8)

  Former smoker

817 (41.8)

212 (21.4)

605 (62.5)

163 (41.8)

305 (41.0)

222 (40.7)

127 (45.9)

56 (45.5)

177 (44.3)

269 (40.2)

  Current smoker

236 (12.1)

73 (7.4)

163 (16.8)

< 0.001

45 (11.5)

105 (14.1)

61 (11.2)

25 (9.0)

0.729

20 (16.3)

48 (12.0)

67 (10.0)

0.057

  ≤ 6 h

697 (35.6)

381 (38.5)

316 (32.6)

141 (36.2)

264 (35.5)

191 (35.0)

101 (36.5)

45 (36.6)

140 (35.0)

237 (35.4)

  6 to ≤ 8 h

1096 (56.0)

517 (52.3)

579 (59.8)

215 (55.1)

412 (55.4)

315 (57.7)

154 (55.6)

65 (52.9)

227 (56.8)

366 (54.7)

  > 8 h

164 (8.4)

91 (9.2)

73 (7.5)

0.003

34 (8.7)

68 (9.1)

40 (7.3)

22 (7.9)

0.929

13 (10.6)

33 (8.3)

66 (9.9)

0.863

  ≤ 6 h

600 (30.7)

344 (34.9)

256 (26.5)

128 (32.9)

217 (29.3)

161 (29.5)

94 (34.2)

35 (28.5)

122 (30.7)

208 (31.1)

  6 to ≤ 8 h

1111 (56.9)

517 (52.4)

594 (61.5)

207 (53.2)

431 (58.1)

320 (58.6)

153 (55.6)

69 (56.1)

233 (58.5)

362 (54.2)

  > 8 h

241 (12.4)

125 (12.7)

116 (12.0)

< 0.001

54 (13.9)

94 (12.7)

65 (11.9)

28 (10.2)

0.437

19 (15.5)

43 (10.8)

98 (14.7)

0.371

 Diabetes

618 (31.6)

283 (28.6)

335 (34.6)

0.004

118 (30.3)

236 (31.7)

179 (32.8)

85 (30.7)

0.851

30 (24.4)

89 (22.3)

241 (36.0)

< 0.001

 Hypertension

1640 (83.8)

834 (84.3)

806 (83.3)

0.523

326 (83.6)

626 (84.1)

453 (83.0)

235 (84.8)

0.902

96 (78.1)

329 (82.3)

568 (84.9)

0.136

 Hypercholesterolemia

1411 (72.1)

761 (77.0)

650 (67.2)

< 0.001

274 (72.1)

544 (73.5)

380 (71.0)

177 (70.8)

0.742

88 (71.5)

292 (73.0)

487 (72.8)

0.950

 Depressive symptoms

428 (21.9)

314 (31.8)

114 (11.8)

< 0.001

94 (24.1)

154 (20.7)

116 (21.3)

64 (23.1)

0.551

20 (16.3)

81 (20.3)

171 (25.6)

0.025

 Serum potassium (mmol/L)

4.3 ± 0.4

4.3 ± 0.4

4.3 ± 0.4

0.355

4.4 ± 0.4

4.3 ± 0.4

4.28 ± 0.37

4.3 ± 0.4

0.003

4.2 ± 0.4

4.3 ± 0.4

4.3 ± 0.4

0.005

 Serum sodium (mmol/L)

139.4 ± 14.9

139.0 ± 17.1

139.9 ± 12.4

0.219

140.1 ± 12.6

139.1 ± 15.7

139.6 ± 14.5

138.8 ± 16.6

0.492

137.6 ± 2.1

140.2 ± 1.4

142.4 ± 2.1

< 0.001

 Glucose (mmol/L)

6.3 ± 1.7

6.3± 1.6

6.4 ± 1.8

0.056

6.29 ± 1.56

6.34 ± 1.75

6.27 ± 1.64

6.43 ± 1.95

0.582

5.7 ± 0.9

6.0 ± 1.2

6.7 ± 2.0

< 0.001

 Blood urea nitrogen (BUN, mmol/L)

6.6 ± 1.8

6.6 ± 1.7

6.7 ± 1.9

0.791

6.6 ± 1.7

6.7 ± 1.8

6.7 ± 1.9

6.7 ± 1.8

0.980

5.9 ± 1.5

6.1 ± 1.4

7.0 ± 1.9

< 0.001

 SOSM (mmol/L)^a

298.4 ± 24.4

297.6 ± 28.0

299.1 ± 20.2

0.298

299.2 ± 21.6

297.6 ± 26.6

299.3 ± 19.1

296.9 ± 31.1

0.580

292.3 ± 3.6

297.9 ± 1.4

304.1 ± 3.8

< 0.001

 Alcohol intake (g/day)

9.8 ± 13.3

4.0 ± 6.7

15.7 ± 15.6

< 0.001

12.5 ± 16.2

9.8 ± 12.9

8.7 ± 12.2

8.2 ± 11.1

< 0.001

13.3 ± 16.5

11.3 ± 15.3

9.1 ± 13.2

0.002

 Energy intake (kcal/day)

2391.7 ± 541.4

2238.3 ± 493.1

2548.6 ± 543.8

< 0.001

2422.1 ± 559.5

2391.2 ± 530.4

2374.7 ± 549.0

2384.1 ± 30.8

0.611

2400.0 ± 598.1

2342.4 ± 549.3

2365.7 ± 554.4

0.579

 Caffeine intake (mg/day)

33.6 ± 31.8

29.6 ± 27.9

37.6 ± 34.9

< 0.001

38.3 ± 35.2

31.6 ± 29.7

32.6 ± 31.3

34.0 ± 32.6

0.007

35.7 ± 35.1

36.9 ± 35.3

35.8 ± 31.9

0.869

 Mediterranean diet score (17-point)

8.5 ± 2.6

8.8 ± 2.6

8.1 ± 2.6

< 0.001

8.4 ± 2.6

8.3 ± 2.6

8.6 ± 2.6

8.7 ± 2.6

0.0619

8.7 ± 2.7

8.6 ± 2.6

8.6 ± 2.5

0.889

 Drinking water intake (ml/day)

1031.2 ±465.2

1033.1 ± 458.8

1029.3

0.8551

352.9 ± 123.4

892.1 ± 30.1

1300.5 ± 17.3

1829.2 ± 155.7

< 0.001

1036.0 ± 499.2

1034.7 ± 466.6

1044.3 ± 478.8

0.946

 Total fluid intake (ml/day)

1842.4 ± 592.0

1797.2 ± 579.7

1888.7 ± 601.1

0.001

1232.1 ± 454.2

1691.2 ± 388.5

2103.5 ± 406.7

2593.5 ± 413.5

< 0.001

1931.1 ± 643.3

1886.5 ± 662.4

1874.4 ± 646.0

0.672

 Total water intake (ml/day)

2871.1 ± 676.2

2853.5 ± 674.8

2889.2 ± 677.4

0.2434

2241.2 ± 500.9

2709.8 ± 493.7

3146.0 ± 516.0

3646.0 ± 562.8

< 0.001

2947.2 ± 710.1

2869.6 ± 743.4

2852.4 ± 735.2

0.421

 Meets EFSA TWI recommendations

1569 (80.2)

898 (90.8)

671 (69.3)

< 0.001

186 (47.7)

595 (80.0)

512 (93.8)

276 (99.6)

<0.001

99 (80.5)

309 (77.3)

521 (77.9)

0.750

 GCF^c

0.04 ± 0.62

− 0.15 ± 0.61

0.22 ± 0.58

< 0.001

0.10 ± 0.58

0.04 ± 0.64

− 0.03 ± 0.66

0.11 ± 0.55

0.018

0.02 ± 0.67

0.13 ± 0.56

0.01 ± 0.64

0.028

 MMSE

28.14 ± 1.94

27.82 ± 2.18

28.46 ± 1.60

< 0.001

28.33 ± 1.84

28.04 ± 1.98

28.02 ± 2.02

28.36 ± 1.74

0.008

28.23 ± 1.91

28.20 ± 2.09

28.14 ± 2.04

0.824

 CDT

5.81 ± 1.31

5.68 ± 1.38

5.94 ± 1.23

< 0.001

5.83 ± 1.37

5.77 ± 1.31

5.80 ± 1.27

5.86 ± 1.31

0.767

5.75 ± 1.50

5.90 ± 1.27

5.89 ± 1.20

0.481

 VFT-a

15.78 ± 4.74

14.75 ± 4.54

16.82 ± 4.71

< 0.001

16.32 ± 4.54

15.61 ± 4.98

15.49 ± 4.73

16.03 ± 4.31

0.032

15.77 ± 5.04

15.72 ± 4.58

15.62 ± 4.70

0.913

 VFT-p

11.95 ± 4.40

11.31 ± 4.34

12.61 ± 4.36

< 0.001

12.23 ± 4.47

11.93 ± 4.49

11.65 ± 4.41

12.23 ± 3.98

0.145

11.99 ± 4.11

12.19 ± 4.35

11.46 ± 4.32

0.023

 TMT-A

55.17 ± 31.40

61.62 ± 32.56

48.94 ± 28.88

< 0.001

53.73 ± 28.75

57.04 ± 33.21

55.77 ± 32.55

51.02 ± 27.04

0.037

56.72 ± 28.45

54.97 ± 30.33

57.56 ± 36.13

0.474

 TMT-B

136.9 ± 78.4

156.6 ± 82.5

116.8 ± 68.3

< 0.001

129.9 ± 75.4

138.0 ± 79.2

142.9 ± 81.4

132.2 ± 72.6

0.06

153.2 ± 92.3

139.6 ± 81.0

146.4 ± 82.4

0.217

 DST-f

8.66 ± 2.46

8.13 ± 2.32

9.19 ± 2.48

< 0.001

8.61 ± 2.33

8.74 ± 2.48

8.50 ± 2.57

8.86 ± 2.34

0.23

8.26 ± 2.62

8.74 ± 2.44

8.73 ± 2.53

0.176

 DST-b

5.06 ± 2.20

4.53 ± 1.97

5.58 ± 2.28

< 0.001

5.04 ± 2.25

5.15 ± 2.15

4.85 ± 2.20

5.27 ± 2.19

0.049

4.89 ± 2.30

5.11 ± 2.11

5.02 ± 2.16

0.638