Objectively Measured Sedentary Time May Predict Insulin Resistance Independent of Moderate- and Vigorous-Intensity Physical Activity
Hendrik J.F. Helmerhorst
Katrien Wijndaele
Sren Brage
Nicholas J. Wareham
Ulf Ekelund
OBJECTIVE-To examine the prospective association between objectively measured time spent sedentary and insulin resistance and whether this association is independent of moderate- and vigorous-intensity physical activity (MVPA) and other relevant confounders. RESEARCH DESIGN AND METHODS-This was a population-based study (Medical Research Council Ely study) in 376 middle-aged adults (166 men; 210 women) over 5.6 years of follow-up. Physical activity and sedentary time were measured objectively by individually calibrated minute-by-minute heart rate monitoring at both baseline and follow-up. Sedentary time was calculated as the heart rate observations (in minutes) below an individually predetermined threshold (flex heart rate) and expressed as a percentage of total monitored time during waking hours over 4 days. The percentage of time spent above 1.75 resting heart rate represented MVPA. Fasting plasma insulin was used as a surrogate measure of insulin resistance. RESULTS-Time spent sedentary at baseline was significantly and positively associated with log fasting insulin at follow-up ( 0.003, 95% CI 0.0006 - 0.006, P 0.015) independent of baseline age, sex, fat mass, fasting insulin, smoking status, and follow-up time. After further adjustment for MVPA, this association was somewhat strengthened ( 0.004, 95% CI 0.0009 - 0.006, P 0.009). CONCLUSIONS-Time spent sedentary predicts higher levels of fasting insulin independent of the amount of time spent at moderate- and vigorous-intensity activity levels. This highlights the importance of reducing sedentary time in order to improve metabolic health, possibly in addition to the benefits associated with a physically active lifestyle. Diabetes 58:1776-1779, 2009
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I
nsulin resistance is a precursor of type 2 diabetes
and a major characteristic of the metabolic
syndrome (1). Hyperinsulinemia and impaired insulin
sensitivity are common clinical findings yielding
independent health risks, including metabolic,
cardiovascular, and neoplastic disorders (2 4).
Several etiological factors have been identified for
impaired insulin sensitivity, including genotype, body
composition, inflammation, and lifestyle factors (57). Low
levels of physical activity and lack of moderate- and
vigorous-intensity physical activity (MVPA) are associated
with insulin resistance (8,9).
Sedentary time has been linked to various
cardiometabolic health outcomes, sometimes independent of overall
physical activity in cross-sectional analyses (10 12).
Because the cardiometabolic consequences are suggested to
be a unique feature in hazardous physical activity
behavior, sedentary behavior should be considered distinctively
from physical activity when examining associations with
these health outcomes (13).
A recent prospective analysis suggested that MVPA but
not sedentary time was associated with insulin resistance
in high-risk individuals over a 1-year follow-up period (14).
Further prospective research is needed to examine these
associations and the direction of causality in normal-risk
populations with longer duration of follow-up. Therefore,
the purpose of the present study was to 1) examine the
prospective association between objectively measured
sedentary time and fasting insulin, a marker of insulin
resistance, in healthy middle-aged Caucasian subjects and
2) examine whether this association is independent of
MVPA and other confounding variables.
RESEARCH DESIGN AND METHODS
This study is part of the Medical Research Council Ely study, a prospective
population-based cohort study of the etiology and pathogenesis of type 2
diabetes and related metabolic disorders. Data were collected in 1994 1996
(baseline) and again in 20012003 (median follow-up time 5.6 years). A total of
393 participants with complete data on anthropometry, body composition, and
physical activity energy expenditure (PAEE) at both baseline and follow-up
were initially selected (15). Participants with missing data on fasting plasma
insulin, fat mass, smoking status, or MVPA were excluded. Therefore, the
present report comprises 376 (166 male) healthy middle-aged Caucasian
subjects. Missing data were random with respect to body composition and
physical activity at baseline. Ethics permission for the study was granted by
the Cambridge Local Research Committee, and all participants provided
written informed consent.
Plasma insulin, glucose, and confounding variables. Data collection
procedures have been described in detail previously (9,16). In brief, blood
samples were taken after an overnight fast. Plasma insulin and glucose levels
were determined using standardized protocols. Levels of fasting plasma
insulin were used as a surrogate measure for insulin resistance. The
homeostasis model assessment of insulin resistance (HOMA-IR) score was
calculated by dividing the product of fasting plasma insulin (microunits per
milliliter) and fasting (...truncated)