Table 1.

Descriptive statistics of the study variables for all twins and the subsample of twins with information on biological ageing

	All twins (n = 22,750)		Subsample (n = 1,153)
	n	Mean (SD) or %	n	Mean (SD) or %
Sex
Female	11,308	49.7	933	80.9
Male	11,442	50.3	220	19.1
Age in 1975	22,750	30.0 (8.9)	1,153	33.2 (9.7)
Zygosity
Unsure	1,902	8.4	-
Monozygotic	6,462	28.4	610	52.9
Same-sex dizygotic	14,386	63.2	543	47.1
Health status in 1981
Diseasesa	18,113		1,055
No	17,018	67.7	1,012	95.9
Yes	1,095	32.3	43	4.1
Latest education in 1981 (in years)	22,205	8.5 (3.2)	1,131	9.2 (3.5)
Leisure-time physical activity
Metabolic equivalent (MET) index (h/day)
in 1975	20,984	2.4 (3.1)	1,116	2.2 (2.5)
in 1981	20,165	2.6 (3.1)	1,098	2.4 (2.4)
in 1990	12,312	3.3 (3.4)	841	3.1 (2.8)
Lifestyle-related factors in 1981
Body mass index (kg/m2)	20,074	23.5 (3.4)	1,097	23.4 (3.4)
Smoking	19,850		1,153
Never	8,932	45.0	703	64.8
Occasional	624	3.1	33	3.0
Former	4,149	20.9	182	16.8
Light	1,476	7.4	53	4.9
Medium	2,714	13.7	77	7.1
Heavy	1,955	9.8	37	3.4
Alcohol useb	19,818		1,091
Never	1,768	8.9	167	15.3
Former	1,092	5.5	69	6.3
Occasional	1,045	5.3	77	7.1
Low	14,337	72.3	746	68.4
Medium	961	4.8	20	1.8
High	398	2.0	10	0.9
Very high	217	1.1	2	0.2
Outcomes
Deaths (1991–2020)	6,949	30.6	267	23.2
Biological ageing
Age at blood draw	-		1,153	63.5 (9.1)
PC-based DNAm GrimAge (in years)			1,153	70.9 (7.3)
DunedinPACE (year/calendar year)	-		1,153	0.98 (0.12)

SD, standard deviation; DNAm, DNA methylation; PC, principal component.

^aSelf-reported physician-diagnosed angina pectoris, myocardial infarction, or diabetes in 1975 or 1981.

^bHigh and very high classes were combined for further analysis.