Adiposity and TV viewing are related to less bone accrual in young children

Abstract

Objective: To examine the relation between baseline fat mass and gain in bone area and bone mass in preschoolers studied prospectively for 4 years, with a focus on the role of physical activity and TV viewing.

Study design: Children were part of a longitudinal study in which measures of fat, lean and bone mass, height, weight, activity, and diet were taken every 4 months from ages 3 to 7 years. Activity was measured by accelerometer and TV viewing by parent checklist. We included 214 children with total body dual energy x-ray absorptiometry (Hologic 4500A) scans at ages 3.5 and 7 years.

Results: Higher baseline fat mass was associated with smaller increases in bone area and bone mass over the next 3.5 years (P < .001). More TV viewing was related to smaller gains in bone area and bone mass accounting for race, sex, and height. Activity by accelerometer was not associated with bone gains.

Conclusions: Adiposity and TV viewing are related to less bone accrual in preschoolers.

Figure 1

Selection of children for the current study from the main study.

Figure 2

Least squares means ± SEM for bone area (top) and BMC (bottom) at age 7 y by quartile of fat mass at age 3.5 y, adjusted for bone area or BMC at age 3.5 y, race, sex, exact age, height at age 7 y; and TV viewing. Levels not connected by the same letter are significantly different (p<0.05 Tukey HSD between least squares means). p<0.001 (top) and p<0.01 (bottom) for the effect of the continuous variable for fat mass at age 3.5 y in the final model (Table II).

Figure 3

The upper edge of each bar represents the least squares mean ± SEM for bone area (top) and BMC (bottom) at age 7 y, adjusted for bone area or BMC at age 3.5 y, race, sex, exact age at baseline and final visit, height at age 7 y, and TV viewing. The lower edge of each bar represents the least squares mean ± SEM for bone area (top) and BMC (bottom) at age 3.5 y, adjusted for race, sex, age, and height. The left two, middle two, and right two bars are the low, medium, and high tertiles for weight at age 3.5 y. Within each tertile, children were classified as above- and below-the-median for fat mass at age 3.5 y. Top: p=0.05 for effect of fat mass group and p=0.5 for effect of weight tertile. Bottom: p=0.2 for effect of fat mass group and p=0.02 for effect of weight tertile. The interaction of fat mass group by weight tertile was not significant for either bone area or BMC (both p>0.7).