Table 3 Characteristics of the participants aged 50–88 years, by study.

From: Dysregulation of the hypothalamic pituitary adrenal (HPA) axis and cognitive capability at older ages: individual participant meta-analysis of five cohorts

Variable

CaPS

LASA

NCDS

NSHD

Whitehall II

N

771

1151

4824

1165

2936

Gender (% male)

100

48.7

51.7

45.4

75.3

Age (years)

73.2 (4.0)

75.1 (6.4)

50.7 (0.15)

63

61.1 (5.9)

BMI (Kg/m2)

27.8 (3.9)

26.9 (4.2)

27.3 (4.8)

27.9 (4.8)

26.7 (4.3)

Current smoker (%)

13.6

18.1

17.9

16.5

7.8

Lower SEP (%)

60.4

39.9

33.4

25.2

53.5

Serum morning cortisol (nmol/L)

—

497.9 (170.8)

—

—

—

Salivary cortisol (nmol/L)

T1 morning

19.6 (10.1)

—

21.2 (11.2)

23.4 (9.8)

20.0 (8.1)

T2

3.6 (5.5)

—

8.3 (7.1)

3.2 (3.4)

2.4 (2.7)

Crystallised ability

NART

28.0 (11.1)

—

—

35.9 (8.8)

—

Mill Hill

—

—

—

—

25.1 (4.2)

GIT vocabulary test

—

12.9 (4.0)

—

—

—

Fluid ability

Verbal fluency

17.7 (5.0)

—

22.6 (6.2)

—

15.6 (3.8)

Verbal Memory

(i) AVLT

—

19.5 (6.2)

—

24.8 (5.8)

6.9 (2.4)

(ii) Coding Task

—

23.4 (7.1)

—

—

—

(iii) Immediate memory

—

—

6.7 (1.5)

—

—

Processing Speed

—

—

335.8 (88.2)

265.5 (69.9)

—

Reaction Time (s)

0.69 (0.20)

—

—

0.62 (0.09)

—

Verbal and mathematical reasoning

26.3 (10.4)

—

—

—

44.2 (10.9)

Non verbal reasoning

—

17.3 (4.5)

—

—

—

  1. Results are presented as mean (SD), unless otherwise stated and are complete data including confounders and morning and night time cortisol measures (where available) and crystallised and fluid cognitive capability.
  2. Serum cortisol level is a morning sample in LASA.
  3. T1 salivary morning cortisol in CaPS, NSHD and Whitehall II was computed as the mean of the waking and 30 minute samples. In NCDS T1 was the 45 minutes after waking sample. In CaPS, NSHD and Whitehall II T2 was the night time cortisol sample and in NCDS it was the 3 hours 45 minutes after waking sample.
  4. See methods for detailed descriptions of crystallised capability and fluid cognition measures. Crystallised capability is the National Adult Reading Test (NART) (0–50) in CaPS and NSHD, the Mill Hill Vocabulary Test (0–33) in Whitehall II and the GIT-vocabulary test in LASA. Fluid capability is derived by factor analysis of the fluid cognition measures in each of the cohorts. Fluid cognition measures in CaPS are animal naming, Alice Heim test (AH4) and reaction time (loge); Coding task, Auditory Verbal Learning Test (AVLT) or Verbal Memory and Ravens Coloured Progressive Matrices (RCPM) in LASA; Verbal memory (15 item word recall over 3 trials), search speed (0–600) and choice reaction time in NSHD and animal naming, verbal memory (20 item word recall) and AH4 in Whitehall II.
  5. Across the cohorts, there was no standard method for classifying socioeconomic position. In CaPS, NCDS and NSHD, lower socioeconomic position was classified as manual (skilled manual, semi-skilled manual and unskilled) and higher socioeconomic position as non-manual (professional, managerial or skilled non-manual). In LASA, lower socioeconomic position was classified as low education level attained and higher socioeconomic position as middle and high education level attained. In Whitehall II, lower socioeconomic position was employment grade 1 and 2 and higher socioeconomic position was employment grade 3.
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