Winning Combination To
Build Bone Density In Children:
Calcium Intake And Vigorous Daily Exercise
BETHESDA, Md. – September 27, 2004 – Prepubescence is a
critical time for building bone mass in children. Strong bones are
important for obvious reasons in growth and development. It is widely
accepted that calcium intake and physical activity are two ways one can
positively impact bone density. But consuming the FDA recommended 800
milligrams of calcium per day, roughly the equivalent of three 8 oz. glasses
of milk, or solely engaging in physical activity isn’t enough to help kids
in this age group retain the maximum amount of bone mass.
Researchers at the University of Wales and the
University of Exeter, United Kingdom, suggest that the combination
of high calcium intake and vigorous exercise is the key to optimal increases
in bone density.
Few studies have examined the interactive effects of
calcium intake and activity, especially ones that differentiate between the
types of activity that most positively affect bone density. But the study
“Interactive effects of habitual physical activity and calcium intake on
bone density in boys and girls” does just that. The authors of the study
are Ann V. Rowlands and Sarah M. Powell, of the University of Wales School
of Sport, Health and Exercise, Roger G. Eston of the Children’s Health and
Exercise Research Centre, University of Exeter, and David K. Ingledew of the
University of Wales School of Psychology. The results of their study appear
in the October 2004 edition of the Journal of Applied Physiology.
Using food diaries and accelerometers, the researchers
were able to track the behavior of 38 girls and 38 boys between the ages of
8 and 11. They observed that the synergistic effect of high levels of
calcium intake and vigorous (as opposed to moderate or low-intensity)
activity were the most effective in building and retaining bone mass. Their
evidence indicates that children should engage in 25 to 40 minutes of
vigorous activity and intake at least 700-800 milligrams of dietary calcium
per day.
For this study, vigorous activity could include actions
like running, playing tag, jumping rope, etc. “You don't have to jump rope
for half an hour. That would be considered very hard. In reality we are
talking about the sort of energy you would expect kids to expend when
playing around outside with a ball or rope,” said Dr. Eston. “A brisk walk
at about 4 mph would do the trick. We are talking about raising the resting
energy levels by about 6-8 times. The idea is to 'accumulate' this sort of
energy expenditure over the day to total about half an hour,” he added.
Abstract
The purpose of this study
was to assess the interactive effects of habitual physical activity (total
and vigorous intensity) and calcium intake on bone mineral content (BMC) in
prepubertal boys and girls.
Seventy-six children, 8 to
11 years old, wore accelerometers for up to 7 days to assess activity.
Calcium intake was estimated by a 4-day weighted food diary. BMC and areal
density (bone mineral density) were measured at the total body, proximal
femur, and femoral neck by using dual-energy X-ray absorptiometry. Moderated
regression analyses were used to assess the contributions of physical
activity (total and vigorous) and calcium intake to BMC, residualized for
bone area and body mass.
Interactive effects of
vigorous activity (≥6 metabolic equivalents) and calcium intake were found
at the total body in boys (b = 2.90 x 10-3) and in girls (b =
6.58 x 10-3) and at the proximal femur (b = 9.87 x 10-5) and femoral
neck (b = 2.29 x 10-5; where b is the regression coefficient
from final equation) in boys only.
Residualized BMC was
high only if both vigorous activity and calcium intake were high.
There were no interactive effects of total (as opposed to vigorous) activity
and calcium intake. This study provides evidence for synergistic action of
habitual vigorous activity and calcium intake on bone mass in children.
Recommendations for optimizing bone mass should reflect this synergism.
Source:
The article “Interactive effects of habitual physical activity and
calcium intake on bone density in boys and girls”
appears in the October issue of the Journal of Applied
Physiology, published by the American
Physiological Society. A copy of the abstract is available to the
public at
www.the-aps.org.
Editors’ note:
A copy of the research paper by Rowlands et al is available to the media.
Members of the media are encouraged to obtain an electronic version and to
interview members of the research team. To do so, please contact Stacy
Brooks in the APS Communications Office (301-634-7253 or
sbrooks@the-aps.org).
Upcoming APS Intersociety
Meeting:
INTEGRATIVE BIOLOGY OF
EXERCISE MEETING - Oct. 6-9, 2004 - Austin, Texas (Co-sponsored by
the American Physiological Society, Canadian Society for Exercise Physiology
and the American College of Sports Medicine.) The meeting schedule can be
found at (http://www.the-aps.org/meetings/aps/austin/tentative.pdf).
The complete program, including abstracts, for the entire meeting is
available upon request to members of the media.
Arrangements to attend the meeting, and for on-site or telephone interviews,
can be made by contacting Donna Krupa (cell: 301.332.4402,
dkrupa@the-aps.org) or Stacy Brooks
(301.634.7253 (sbrooks@the-aps.org)
in the APS Communications Office.
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