230 Introduction to Human Nutrition
intake are enamel and skeletal fl uorosis. Enamel
fl uorosis is a dose-related effect caused by fl uoride
ingestion during the pre-eruptive development of the
teeth. After the enamel has completed its pre-eruptive
maturation, it is no longer susceptible. Inasmuch as
enamel fl uorosis is regarded as a cosmetic effect, it is
the anterior teeth that are of most concern. The pre-
eruptive maturation of the crowns of the anterior
permanent teeth is fi nished and the risk of fl uorosis
is over by 8 years of age. Therefore, fl uoride intake up
to the age of 8 years is of most interest. Mild fl uorosis
(which is not readily apparent) has no effect on tooth
function and may render the enamel more resistant
to caries. In contrast, the moderate and severe forms
of enamel fl uorosis are generally characterized by
esthetically objectionable changes in tooth color and
surface irregularities.
Skeletal fl uorosis has been regarded as having three
stages. Stage 1 is characterized by occasional stiffness
or pain in joints and some osteosclerosis of the pelvis
and vertebrae, whereas the clinical signs in stages 2
and 3, which may be crippling, include dose-related
calcifi cation of ligaments, osteosclerosis, exostoses,
and possibly osteoporosis of long bones, muscle
wasting, and neurological defects owing to hypercal-
cifi cation of vertebrae. The development of skeletal
fl uorosis and its severity are directly related to the
level and duration of exposure. Most epidemiological
research has indicated that an intake of at least 10 mg/
day for 10 or more years is needed to produce the
clinical signs of the milder form of the condition.
Crippling skeletal fl uorosis is extremely rare. For
example, only fi ve cases have been confi rmed in the
USA since the mid-1960s.
Based largely on the data on the association of high
fl uoride intakes with risk of skeletal fl uorosis in chil-
dren (>8 years) and adults, the US Food and Nutri-
tion Board has established a tolerable UL of fl uoride
of 10 mg/day for children (>8 years), adolescents, and
adults, as well as pregnant and lactating women.
Assessing status
A high proportion of the dietary intake of fl uoride
appears in urine. Urinary output in general refl ects
the dietary intake.
Requirements and dietary sources
Most foods have fl uoride concentrations well below
0.05 mg/100 g. Exceptions to this observation include
fl uoridated water, beverages, and some infant formu-
lae that are made or reconstituted with fl uoridated
water, teas, and some marine fi sh. Because of the
ability of tea leaves to accumulate fl uoride to concen-
trations exceeding 10 mg/100 g dry weight, brewed
tea contains fl uoride concentrations ranging from 1
to 6 mg/l depending on the amount of dry tea used,
the water fl uoride concentration and brewing time.
Intake from fl uoridated dental products adds
considerable fl uoride, often approaching or exceeding
intake from the diet, particularly in young children
who have poor control of the swallowing refl ex. The
major contributors to nondietary fl uoride intake
are toothpastes, mouth rinses, and dietary fl uoride
supplements.
In 1997 the US Food and Nutrition Board estab-
lished AI values for fl uoride: infants 0.01 mg (fi rst 6
months), 0.5 mg (7–12 months), children and adoles-
cents 0.7, 1.0, and 2.0 mg (1–3, 4–8, and 9–13 years,
respectively), male adolescents and adults 3 and 4 mg
(14–18 and 19 years and older, respectively), female
adolescents and adults 3 mg (over 14 years, including
pregnancy and lactation). The AI is the intake value
of fl uoride (from all sources) that reduces the occur-
rence of dental caries maximally in a group of indi-
viduals without causing unwanted side-effects. With
fl uoride, the data are strong on caries risk reduction
but the evidence upon which to base an actual require-
ment is scant, thus driving the decision to adopt an
AI as the reference value.Micronutrient interactions
The rate and extent of fl uoride absorption from the
gastrointestinal tract are reduced by the ingestion of
foods particularly rich in calcium (such as milk or
infant formulae).9.15 Chromium
Chromium has an abundance of 0.033% in the Earth’s
crust. It is a transition element that can occur in a
number of valence states, with 0, +2, +3, and +6 being
the most common. Trivalent chromium is the most
stable form in biological systems. The principal ore is
chromite. Chromium is used to harden steel, to
manufacture stainless steel, and to form many useful
alloys. It fi nds wide use as a catalyst. Hexavalent chro-
mium is a strong oxidizing agent that comes primarily
from industrial sources.