Smoking and perceived stress in relation to short salivary telomere length among caregivers of children with disabilities

Figures & data

Table 1. Characteristics of 89 caregivers of children with disabilities, according to salivary telomere length status.

	Total	Short TL (n = 22)	Long TL (n = 67)
	(n = 89)	Quartile 1 (0.39–0.72)	Quartile 2–Quartile 4 (0.73–2.10)
	n (%)/mean (SD)	n (%)/mean (SD)	n (%)/mean (SD)	p value
Sex
Men	12 (13.5)	4 (18.2)	8 (11.9)	0.481
Women	77 (86.5)	18 (81.8)	59 (88.1)
Age, mean (SD), years	43.1 (8.7)	46.3 (10.8)	42.1 (7.7)	0.047
Race
Hispanic	66 (74.2)	14 (63.6)	52 (77.6)	0.194
Indigenous	23 (25.8)	8 (36.4)	15 (22.4)
Marital status
Married/living with a partner	60 (67.4)	16 (72.7)	44 (65.7)	0.540
Other	29 (32.6)	6 (27.3)	23 (34.3)
Employment
No	40 (44.9)	9 (40.9)	31 (46.3)	0.661
Yes	49 (55.1)	13 (59.1)	36 (53.7)
Education
<High school	40 (44.9)	12 (54.6)	28 (41.8)	0.263
High school	25 (28.1)	18 (31.8)	18 (26.9)
> High school	24 (27.0)	3 (13.6)	21 (31.3)
BMI, mean (SD), kg/m^2	29.8 (5.1)	30.6 (5.9)	29.6 (4.8)	0.474
Obesity status
BMI < 30 kg/m^2	59 (66.3)	13 (59.1)	46 (68.7)	0.410
BMI ≥30 kg/m^2	30 (33.7)	9 (40.9)	21 (31.3)
Waist-to-hip ratio, mean (SD)	0.89 (0.08)	0.91 (0.08)	0.89 (0.09)	0.186
Medication use
No	56 (62.9)	14 (63.6)	42 (62.7)	0.936
Yes	33 (37.1)	8 (36.4)	25 (37.3)
Alcohol consumption
No	72 (80.9)	20 (90.9)	52 (77.6)	0.221
Yes	17 (19.1)	2 (9.1)	15 (22.4)
Current smoking
No	50 (56.2)	8 (36.4)	42 (62.7)	0.031
Yes	39 (43.8)	14 (63.6)	25 (37.3)
Perceived stress
Low stress (PSS-14 score <27)	65 (73.0)	12 (54.6)	53 (79.1)	0.024
High stress (PSS-14 score ≥27)	24 (27.0)	10 (45.5)	14 (20.9)
Joint effect of smoking and perceived stress
Non-smoker with low perceived stress	41 (46.1)	6 (27.3)	35 (52.2)	0.031
Non-smoker with high perceived stress	9 (10.1)	2 (9.1)	7 (10.5)
Smoker with low perceived stress	24 (27.0)	6 (27.3)	18 (26.9)
Smoker with high perceived stress	15 (16.9)	8 (36.4)	7 (10.5)
Diagnosis of children’s disability
Diagnosis 1	28 (31.5)	9 (40.9)	19 (28.4)	0.295
Diagnosis 2	19 (21.4)	2 (9.1)	17 (25.4)
Diagnosis 3	26 (29.2)	8 (36.4)	18 (26.9)
Diagnosis 4	16 (18.0)	3 (13.6)	13 (19.4)

TL = telomere length; SD = standard deviation; BMI = body mass index; PSS = Perceived Stress Scale. Student t-test was conducted for continuous variables, while Fisher's test (when the sample size in a cell <5) or chi-square test was conducted for categorical variables. The 14-item Perceived Stress Scale (PSS-14) was used to define low stress (PSS-14 score <27) and high stress (PSS-14 score ≥27). Based on the International Classification of Diseases 10th revision (ICD-10), the diagnosis of children’s disabilities was classified as: (1) Diagnosis 1: Mental and behavioral disorders (e.g. autism, attention deficit hyperactivity disorder, mental retardation); (2) Diagnosis 2: Diseases of the musculoskeletal system and connective tissue, skin and subcutaneous tissue (e.g. scoliosis); (3) Diagnosis 3: Diseases of the nervous system (e.g. cerebral palsy); (4) Diagnosis 4: Congenital malformations, deformations and chromosomal abnormalities (e.g. Down syndrome).

Figure 1. Scatter plot of age by relative salivary telomere length among 89 caregivers of children with disabilities. Pearson correlation coefficient (log-transformed TL and age): r = −0.29; p = 0.006.

Table 2. Linear and logistic regression models: associations between current smoking and salivary telomere length among 89 caregivers of children with disabilities.

Outcome variable: log-transformed TL	β (SE)	p value	R-square	R-square Adjusted
Linear regression model
Model 1: unadjusted	−0.058 (0.027)	0.036	0.050	0.039
Model 2: adjusted for age	−0.067 (0.026)	0.012	0.148	0.128
Model 3: adjusted for age and perceived stress	−0.060 (0.027)	0.028	0.164	0.135
Outcome variable: shorter TL	OR (95% CI)	p value
Logistic regression model
Model 1: unadjusted	2.94 (1.08, 7.99)	0.035
Model 2: adjusted for age	3.61 (1.25, 10.41)	0.018
Model 3: adjusted for age and perceived stress	3.17 (1.05, 9.52)	0.041

TL = telomere length; SE = standard error; OR = odds ratio; 95% CI = 95% confidence interval. Age was a continuous variable. Shorter telomere length was defined as the lowest quartile of salivary telomere length (TL < 0.73) vs. TL ≥ 0.73. The 14-item Perceived Stress Scale (PSS-14) was used to define low levels of perceived stress (score <27) and high levels of perceived stress (score ≥27).

Table 3. Linear and logistic regression models: associations between perceived stress and salivary telomere length among 89 caregivers of children with disabilities.

Outcome variable: log-transformed TL	β (SE)	p value	R-square	R-square Adjusted
Linear regression model
Model 1: unadjusted	−0.047 (0.031)	0.131	0.026	0.015
Model 2: adjusted for age	−0.053 (0.030)	0.078	0.115	0.095
Model 3: adjusted for age and current smoking	−0.038 (0.030)	0.204	0.163	0.135
Outcome variable: shorter TL	OR (95% CI)	p value
Logistic regression model
Model 1: unadjusted	3.16 (1.13, 8.80)	0.028
Model 2: adjusted for age	3.65 (1.25, 10.66)	0.018
Model 3: adjusted for age and current smoking	3.13 (1.03, 9.55)	0.045

TL = telomere length; SE = standard error; OR = odds ratio; 95% CI = 95% confidence interval. Age was a continuous variable. Shorter telomere length was defined as the lowest quartile of salivary telomere length (TL < 0.73) vs. TL ≥ 0.73. The 14-item Perceived Stress Scale (PSS-14) was used to define low levels of perceived stress (score <27) and high levels of perceived stress (score ≥27).

Figure 2. Means of relative salivary telomere length and standard errors across current smoking and perceived stress groups. As the value of salivary telomere length was not normally distributed, the natural logarithm of salivary telomere length data was transformed. The means of salivary telomere length were presented because these values were more meaningfully interpreted than transformed values. Analysis of variance (ANOVA) was conducted to test the differences in log-transformed TL across current smoking and perceived stress groups.

Table 4. Linear and logistic regression models: associations of current smoking and perceived stress with salivary telomere length among 89 caregivers of children with disabilities.

Outcome variable:	Smoker with high stress		Smoker with low stress		Non-smoker with high stress		R-square	R-square Adjusted
log-transformed TL	β (SE)	p value	β (SE)	p value	β (SE)	p value
Linear regression model
Model 1: unadjusted	−0.096 (0.039)	0.014	−0.034 (0.033)	0.300	0.001 (0.047)	0.979	0.074	0.041
Model 2: adjusted for age	−0.113 (0.037)	0.003	−0.037 (0.031)	0.237	0.009 (0.044)	0.836	0.184	0.145
Outcome variable: shorter TL	OR (95% CI)	p value	OR (95% CI)	p value	OR (95% CI)	p value	p value for interaction term
Logistic regression model
Model 1: unadjusted	6.67 (1.76, 25.30)	0.005	1.94 (0.55, 6.90)	0.303	1.67 (0.28, 10.03)	0.577	0.531
Model 2: adjusted for age	10.59 (2.36, 47.55)	0.002	2.29 (0.60, 8.66)	0.224	1.73 (0.28, 10.84)	0.559	0.408

TL = telomere length; SE = standard error; OR = odds ratio; 95% CI = 95% confidence interval. Age was a continuous variable. Shorter telomere length was defined as the lowest quartile of salivary telomere length (TL < 0.73) vs. TL ≥ 0.73. The 14-item Perceived Stress Scale (PSS-14) was used to define low stress (score <27) and high stress (score ≥27). Caregivers who were non-smokers with lower stress served as the reference group in the models. The interaction term (smoking*perceived stress) was added to each model to examine whether there was an interaction between current smoking and perceived stress with shorter salivary TL.