No abstract

Valid assessment of physical activity is important to researchers and practitioners interested in surveillance, screening, programme evaluation and intervention. The validity of an assessment instrument is commonly considered its most important attribute. Convergent validity is the extent to which an instrument's output is associated with that of other instruments intended to measure the same exposure of interest. A systematic review of the literature produced 25 articles directly relevant to the question of convergent validity of pedometers against accelerometers, observation, and self-reported measures of physical activity. Reported correlations were pooled and a median r-value was computed. Pedometers correlate strongly (median r = 0.86) with different accelerometers (specifically uniaxial accelerometers) depending on the specific instruments used, monitoring frame and conditions implemented, and the manner in which the outputs are expressed. Pedometers also correlate strongly (median r = 0.82) with time in observed activity. Time in observed inactivity correlated negatively with pedometer outputs (median r = -0.44). The relationship with observed steps taken depended upon monitoring conditions and speed of walking. The highest agreement was apparent during ambulatory activity (running, walking) or during sitting (when both observation and pedometers would register few steps taken). There was consistent evidence of reduced accuracy during slow walking. Pedometers correlate moderately with different measures of energy expenditure (median r = 0.68). The relationship between pedometer outputs and energy expenditure is complicated by the use of many different direct and indirect measures of energy expenditure and population samples. Concordance with self-reported physical activity (median r = 0.33) varied depending upon the self-report instrument used, individuals assessed, and how pedometer outputs are expressed (e.g. steps, distance travelled, energy expenditure). Pedometer output has an inverse relationship with reported time spent sitting (r = -0.38). The accumulated evidence herein provides ample support that the simple and inexpensive pedometer is a valid option for assessing physical activity in research and practice.

OBJECTIVE -Accumulating research suggests low-circulating vitamin D concentrations, i.e., 25-hydroxyvitamin-D [25(OH)D], may be associated with an increased prevalence of metabolic syndrome; however, previous studies have not accounted for parathyroid hormone (PTH) levels. We examined the association of 25(OH)D and PTH with the prevalence of metabolic syndrome in a community-based cohort of older adults. RESULTS -In men, there was a significant trend (P ϭ 0.03) of increasing adjusted odds for metabolic syndrome with increasing PTH concentrations, primarily due to an odds ratio of 2.02 (95% CI 0.96 -4.24) in men in the top quintile (Ն63 ng/l) of PTH concentration. This association remained unchanged after taking into account 25(OH)D levels and excluding men with diabetes or impaired renal function; it was attenuated after adjustment for the homeostasis model assessment of insulin resistance. Neither PTH in women nor 25(OH)D levels in either sex was related to the metabolic syndrome. RESEARCH DESIGN AND METHODSCONCLUSIONS -These findings suggest an increased risk of metabolic syndrome with elevated PTH levels in older men and no effect of 25(OH)D concentrations in either sex. The reason for the sex difference in the PTH-metabolic syndrome association is unknown. Prospective studies are necessary to better determine the roles of 25(OH)D and PTH in the etiology of metabolic syndrome. Diabetes Care 30:1549-1555, 2007D ecreased vitamin D and elevated parathyroid hormone (PTH) levels may play a role in the etiology of metabolic syndrome, either through an association with individual components of metabolic syndrome or via insulin resistance (1,2). Vitamin D levels have been shown to be inversely related both with fasting glucose concentrations (3-5) and adiposity (6 -10) and have been suspected to be involved in the regulation of blood pressure, based on blood pressure reduction with vitamin D 3 supplementation in patients with essential hypertension (11,12). Other evidence suggests a role for vitamin D in maintaining normal insulin synthesis and secretion (13,14). Vitamin D and PTH are both responsible for maintaining extracellular calcium homeostasis (19). Vitamin D increases the efficiency of intestinal calcium absorption, and PTH is secreted in response to low-circulating calcium concentrations. Elevated PTH secondary to low vitamin D increases calcium resorption from the skeleton at the expense of an increased risk of fracture (20). Secondary hyperparathyroidism may also increase the risk of developing components of metabolic syndrome, including hypertension (21-26), obesity (6,9,10,27-29), and diabetes (30 -32). However, we are unaware of previous research investigating whether PTH levels are also associated with the metabolic syndrome.Previous studies linking low 25(OH)D with an increased prevalence of metabolic syndrome (1,18) were limited by their inability to simultaneously account for PTH, since both vitamin D and PTH operate within a tightly controlled feedback system to maintain extracellular calcium conce...

OBJECTIVE Evidence on the association of vitamin D with cardiovascular risk factors in youth is very limited. We examined whether low serum vitamin D levels [25(OH)D] are associated with cardiovascular risk factors in US adolescents aged 12–19 years. METHODS Cross-sectional analysis of 3,577 fasting, nonpregnant adolescents without diagnosed diabetes who participated in the 2001–2004 National Health and Nutrition Examination Survey (NHANES). Risk factors for cardiovascular disease measured using standard methods and defined according to age-modified Adult Treatment Panel-III definitions. RESULTS Mean 25(OH)D in US adolescents was 24.8 ng/mL; lowest in black (15.5 ng/mL), intermediate in Mexican American (21.5 ng/mL), and highest in white (28.0 ng/mL) adolescents (p<0.001, for each pair-wise comparison). Low 25(OH)D levels were strongly associated with overweight status and abdominal obesity (ptrend<0.001, for both). Following adjustment for age, sex, race/ethnicity, body mass index, socioeconomic status, and physical activity, 25(OH)D levels were inversely associated with systolic blood pressure (p=0.02) and plasma glucose concentrations (p=0.01). The adjusted odds ratio (95% CI) for those in the lowest (<15 ng/mL) compared to the highest quartile (>26 ng/mL) of 25(OH)D for hypertension was 2.36 (1.33, 4.19); for fasting hyperglycemia 2.54 (1.01, 6.40); for low HDL-cholesterol 1.54 (0.99, 2.39); for hypertriglyceridemia 1.00 (0.49, 2.04); and for metabolic syndrome 3.88 (1.57, 9.58). CONCLUSIONS Low serum vitamin D in US adolescents is strongly associated with an increased prevalence of hypertension, hyperglycemia, and metabolic syndrome, independent of adiposity. Whether the low concentrations of vitamin D among adolescents predicts future adverse health events remains to be determined.

Non-Hispanic blacks and Hispanics were more inactive during their leisure time than were non-Hispanic whites. Social class but not occupational physical activity seems to moderate the relationship between race/ethnicity and leisure-time physical inactivity.