476
X. Lin et al.
cardiorespiratory fitness (35). Active in-
dividuals tend to exhibit higher cardiore-
spiratory fitness, which is associated with
increased telomere length (36). Savela
et al. reported that men in the highest
physical activity group had the lowest
mortality rate (37). Ludlow et al. found
that moderate levels of physical activity
may have a more protective influence on
telomere length than both low and high
Fig. 4. Meta-analysis of the association between telomere length and moderate exercise.
levels of exercise (34). The inconsistency
95% CI: 95% confidence interval; SD: standard deviation.
in our study could be due to the increased
breadth of physical activity, genetic di-
Sensitivity analyses
versity of participants, and sample size.
Sensitivity analyses were performed to detect influ-
Aerobic exercise is an ordinary physical activity that
ential studies. Table SII lists the pooled mean dif-
is positively associated with telomere length (20, 33,
ferences, with one study at a time removed from the
38). Aerobic exercise can improve maximal oxygen
meta-analysis. Exercise was positively associated with
uptake, which is positively related to telomere length
telomere length regardless of whether any study was
through the activation of telomerase (39). Werner et al.
removed from the meta-analysis.
reported that aerobic endurance subjects (e.g continuous
running) exhibited increased telomerase activity and
telomere-stabilizing proteins compared with untrained
DISCUSSION
controls, which contributes to chromosomal stability
This meta-analysis found that exercise had a positive
and integrity (40).On the other hand, individuals who
effect on telomere length. There are several possible
engaged in long-term aerobic exercise have significantly
reasons for this phenomenon. First, inactivity may re-
improved body mass index and decreased low-density
duce the expression of telomerase reverse transcriptase
lipoprotein values(41), which is beneficial for maintain-
and telomeric repeat-binding factor 2, which could
ing telomere length through the modulation of shelterin
lead to decreased activity of telomerase and telomere
and telomerase dynamics (42, 43). In the current study,
stabilizing protein (27). Secondly, the longer telomere
however, subgroup analysis did not find that aerobic
lengths associated with increased physical activity le-
exercise was positively related to longer telomere length.
vels may be explained by the overall diminished burden
The source of this discrepancy may be attributed to dif-
of oxidative stress and inflammation, such as decreased
ferences in the intensity and duration of aerobic exercise,
levels of high-sensitivity C-reactive protein, inter-
participant genetic diversity, sample size, and physical
leukin-6, tumour necrosis factor-аlpha, granulocyte
activity measurements.
colony-stimulating factor, and F2-isoprostane. These
Some studies have reported a positive relationship
inflammatory indicators have been found to contribute
between longer telomere length and other types of exer-
to telomere attrition (28–30). Thirdly, physical inac-
cise when subgroup analysis was performed according
tivity may increase the risk of insulin resistance and
to type of exercise, such as resistance exercise and
obesity, which may also accelerate telomere attrition
yoga. Resistance exercise is also positively associated
(31, 32). Nevertheless, many studies did not report a
with telomere length, although there has been only
linear relationship between telomere length and inten-
one study reporting the effect of resistance training
sity of exercise (15, 16, 20, 26, 33). These discordant
on telomere length (43). Resistance exercise not only
findings may be due to differences in the methods of
diminished the burden of oxidative stress and inflam-
DNA extraction, telomere measurement, sample size,
mation, but was also associated with a higher level of
and/or genetic differences.
satellite cell recruitment and promoted type II muscle
The current study also found that moderate and ro-
fibre hyperplasia and hypertrophy (44). In addition,
bust exercise had positive effects on telomere length,
individuals with sarcopaenia exhibited lower walking
although the intensity of exercise across these studies
speed and grip strength due to low muscle mass (45,
differed. These results were consistent confirmed in
46). Compared with non-sarcopaenia patients, telomere
many studies (18, 19, 21, 23–25), while other studies
lengths were shorter in older outpatients with sarco-
found that the highest, but not the lowest, levels of
paenia (47). Resistance exercise has been shown to be
activity, had a significant association with telomere
effective in improving sarcopaenia status and reducing
length (26, 34). This result may be explained by higher
the risk of functional decline (48, 49). Yoga, which
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