Table 1.

Summary of studies estimating narrow-sense heritability (h²) of telomere length (TL) in vertebrates. qPCR, quantitative polymerase chain reaction; TRF, telomere restriction fragments; n.s., not significant; MZ, monozygotic twins; DZ, dizygotic twins.

ref.	species	method	Parent and offspring age at sampling controlled for?	Parental age at conception controlled for?	Environment controlled for?	statistics	Na	h2 (95% CI)d
[42]	human Homo sapiens	Southern blot	yes: twins sampled at 4, 17 and 44 years	no	yes: shared environment	MZ twins DZ twins	59 56	0.78 (0.69–0.87) 0.78 (0.69–0.87)
[43]	human Homo sapiens	Southern blot	yes: age as a covariate	no	no	linear mixed model (twin data)	47	0.84
[44]	human Homo sapiens	Southern blot	yes: age-adjusted telomere length	no	telomere length adjusted for smoking	father–son father–daughter mother–son mother–daughter sister–sister sister–brother brother–brother	34 47 51 71 22 25 23	n.s. 1.20 0.82 1.18 1.22 1.42 1.66
[45]	human Homo sapiens	Southern blot	no	no	no	MZ twins (73–79 yr) DZ twins (73–79 yr) MZ twins (80–94 yr) DZ twins (80–94 yr) MZ twins (73–94 yr) DZ twins (73–94 yr)	89 114 39 45 128 159	0.31 0.54 0.34 n.s. 0.32 0.50
			yes: age as a covariate	no	yes: non-shared environment	biometric model (twin data)	287	0.36 (0.22–0.48)
[46]	human Homo sapiens	Southern blot	yes: age as a covariate	no	no	not stated (sibling data)	383 adults /258 sib pairs	0.82 (0.59–1.05)
[47]	human Homo sapiens	qPCR	yes: age-adjusted telomere length	yes: adjusted for parental age at birth	no	father–offspring father–son father–daughter mother– offspring mother–son mother–daughter	42 20 22 41 18 23	1.13 1.08 1.21 n.s. n.s. n.s.
[48]	human Homo sapiens	Southern blot	yes: age as a covariate	no	yes: shared familial environment	structural equation model (twin data)	1025	0.36 (0.18–0.48)
[49]	human Homo sapiens	qPCR	yes: age-adjusted telomere length	no	no	father–son father–daughter mother–son mother–daughter	62 102 63 105	1.12 0.86 n.s. n.s.
			yes: age as covariate	no	yes: environmental risk factors (e.g. age and sex)	‘animal’ model	907	0.44 (0.32–0.56)
[50]	human Homo sapiens	Southern blot	yes: age-adjusted telomere length	no	yes: shared and individual environment	linear mixed model (twin data)	306	n.s.
[51]	human Homo sapiens	Southern blot	no	no	no	linear mixed model (twin data)	175	0.56 (0.42–0.67)
[52]	human Homo sapiens	qPCR	no	no	no	parent–offspring (centenarian parents)	86	0.86
[53]	human Homo sapiens	qPCR	yes: age-adjusted telomere length	no	no	father–son father–daughter mother–son mother–daughter grandparent–grandchild	51 47 57 72 85	0.93 0.97 n.s. 0.59 1.09
[54]	human Homo sapiens	qPCR	yes: age-adjusted telomere length	yes: adjusted for parental age	no	parent–offspring: leukocytes CD34 + cells mononuclear cells buccal cells	not stated	0.90 0.79 1.09 0.74
[55]	human Homo sapiens	qPCR	yes: age as covariate	no	yes: cohort as covariate	parent–offspring	41	1.32
[56]	human Homo sapiens	qPCR	yes: age-adjusted telomere length	no	no	siblings MZ twins DZ twins father–son father–daughter mother–son mother–daughter	1553 2534 2172 791 882 850 1005	0.98 0.69 1.00 0.68 0.66 0.84 0.84
			yes: age as covariate	no	no	meta-analysis (based on estimates from 6 ‘animal’ models)	19 713	0.70 (0.64–0.76)
[57]	human Homo sapiens	qPCR	yes: age as covariate	no	yes: education, site, smoking, alcohol consumption and marital status as covariates	animal model: all data males females	4289 1927 2362	0.54 (0.47–0.61) 0.60 (0.47–0.72) 0.52 (0.42–0.62)
[58]	human Homo sapiens	qPCR	yes: age as covariate	no	no	‘animal’ model	3587	0.56 (0.50–0.61)
[59]	human Homo sapiens	qPCR	yes: age as covariate	no	no	‘animal’ model: all data excluding haematological malignancies	1079 949	0.63 (0.35–0.90) 0.76 (0.46–1.05)
[60]	human Homo sapiens	qPCR	yes: gestational age as covariate	yes: maternal age as covariate	yes: shared and individual environment	structural equation model (twin data)	162	0.13 (0.00–0.69)
[61]	human Homo sapiens	qPCR	no	yes: controlled for parental age	yes: controlled for education	father–ADHD offspring mother–ADHD offspring	37 57	1.26 (0.70–1.82) 1.12 (0.76–1.48)
[62]	human Homo sapiens	Southern blot	yes: age as covariate	no	yes: shared and individual environment	linear mixed model (twin data)	652	0.64 (0.39–0.83)
[63]	human Homo sapiens	qPCR	yes: age as covariate	no	yes: education, site, smoking, alcohol consumption and marital status as covariates	animal model: all data fathers & offspring mothers & offspring fathers & male offspring fathers & female offspring mothers & male offspring mothers & female offspring	3040 3404 3568 1855 2147 2016 2311	0.54 (0.47–0.61) 0.67 (0.58–0.76) 0.61 (0.52–0.69) 0.65 (0.52–0.79) 0.62 (0.50–0.74) 0.57 (0.44–0.69) 0.53 (0.42–0.63)
[64]	human Homo sapiens	not stated	yes: age-adjusted telomere length	no	no	MZ twins	210	0.88
[65]	human Homo sapiens	qPCR	yes: age as covariate	no	yes: education as covariate	‘animal’ model with SNP-based relatedness	3290	0.28 (0.03–0.53)
[66]	human Homo sapiens	qPCR	yes: age-adjusted telomere length	no	no	pairwise familial correlations	1780	0.63
[67]	human Homo sapiens	Southern blot	no: babies < 2 week old, and mothers with babies with Down syndrome or control babies were aged matched	no	no	mother–offspring with Down syndrome (MI) mother–offspring with Down syndrome (MII) mother–offspring (control group)	106 64 186	−0.12 (−0.15 to −0.09) −0.13 (−0.16 to −0.11) −0.16 (−0.20 to −0.11)
[68]	kakapo, Strigops habroptilus	Southern blot	no: but no TL–age correlation	no	no	mother–offspring mother–daughter mother–son father–offspring father–daughter father–son	29 19 10 26 18 8	0.84 n.s. 1.53 n.s. n.s. n.s.
[69]	sand lizard, Lacerta agilis	Southern blot	yes: residuals from TL–age regression	no	no	mother–daughter father–son	55 40	0.52 (0.09–0.95) 1.23 (0.80–1.66)
[70]	collared flycatcher, Ficedula albicollis	qPCR	yes: nestlings sampled at day 12	no	yes: cross-foster brood triplet	‘animal’ model with cross-fostered siblings	359	0.09 (−0.04–0.15)
[71]	King penguin, Aptenodytes patagonicus	qPCR	no: chicks measured at day 10, but parents during brooding	no	no	mid-parent–offspring mother–offspring	53 53	0.2 (−0.02–0.42) 0.2 (0.01–0.39)
[31]	great reed warbler, Acrocephalus arundinaceus	qPCR	yes: TL measured at days 8–10	no	no	mother–mid-offspring mother–mid-daughter mother–mid-son father–mid-offspring father–mid-daughter father–mid-son	17 17 17 19 19 19	1.08 1.12 (0.34–1.90) 1.38 (0.40–2.36) n.s. n.s. n.s.
				yes: maternal age (paternal age had no significant effect)	yes: maternal identityb	‘animal’ model	193	0.48 (0.24–0.72)
[72]	zebra finch, Taeniopygia guttata	TRF	yes: log(age) as covariate	no	yes: family, maternal or paternal identity	full-sibling maternal half-sibling paternal half-sibling	42 8 18	1.18 (0.46–1.90) 1.35 (−1.04–3.74) 0.93 (−0.27–2.13)
					noc	‘animal’ model with cross-fostered siblings	125	0.999 (0.87–1.00)
[73]	white-throated dipper, Cinclus cinclus	qPCR	yes: nestling age at sampling as covariate	no	no	mother–mid-offspring father–mid-offspring mother–mid-offspring father–mid-offspring	59 59 59 59	0.44 (0.048–0.83) 0.08 (−0.35–0.51) 0.44 (0.048–0.83) 0.08 (−0.35–0.51)
					yes: nest and year of birth	‘animal’ model	177	n.s. [0.038 (−0.10–0.17)]

^aN: number of relative pairs in regressions or phenotyped individuals in ‘animal’ models. 95% CI are stated for studies providing these data, or where s.e. was provided this was multiplied by 1.96 to estimate the CI.

^b‘Animal’ model including brood identity did not converge.

^c‘Animal’ models including parental effects did not converge.

^dHeritability estimates calculated from parent–offspring regressions (as the slope divided by the coefficient of relatedness) can mathematically be greater than one, whereas heritability is bound between 0 and 1.