Abstract:
This study was designed to determine whether
dietary protein is a nutritional factor influencing the
bioavailability of dietary fluoride. To accomplish
this, a factorial experiment was conducted with
weanling rats fed a purified diet to determine the
influence of dietary protein type (casein or
lactalbumin) and level (12% or 36%) on fluoride
bioavailability. Dietary fluoride in each case was 2
or 10 ppm supplied as sodium fluoride. After four
weeks, fluoride retention was significantly reduced
(P < 0.001) in rats fed high protein diets at 2 ppm
fluoride, which was reflected in decreased femur and
tibia fluoride concentration. A significant reduction
in total femur fluoride content was observed only for
rats fed diets containing 36% casein and 10 ppm fluoride. Results for molar fluoride content were less
reliable than either femur or tibia in this regard.
This protein-induced reduction of fluoride retention
was observed despite the fact that apparent fluoride
absorption was enhanced in all groups fed high protein
diets (P < 0.001). Urinary excretion of fluoride was
significantly increased in all rats fed high protein
diets, thus accounting for the observed reduction in
skeletal fluoride uptake. Significantly greater
(P < 0.001) body weights were observed among rats fed
high levels of protein than among rats fed normal
protein diets, despite the fact that food intake for
all treatment groups was adequate and similar. No
consistent effect on skeletal or molar fluoride uptake
due to protein type was evident under the conditions of
this study. Although this study was not designed to
investigate the mechanism involved in decreased
fluoride retention with high protein diets, increased
urinary fluoride excretion may be due to increased
glomerular filtration rate coupled with decreased renal
tubular fluoride reabsorption. Therefore, the results
of this study demonstrate that, in the rat, a threefold
increase in dietary protein level negatively influences
fluoride bioavailability by promoting increased urinary
fluoride excretion thus reducing fluoride available for
incorporation into bones and teeth. These results suggest that excess dietary protein consumption common
in the U.S. combined with marginal fluoride intake may
adversely affect fluoride bioavailability in humans.
This could reduce the fluoride content of teeth and
bones, which may decrease resistance to dental caries
and compromise skeletal integrity.
