Minerals and Trace Elements 231Absorption, transport, and
tissue distribution
The human body contains only a small amount of
chromium, less than 6 mg. The kidney, followed
by the spleen, liver, lungs, heart, and skeletal muscle
are the tissues with the greatest chromium
concentrations.
Absorbed chromium is excreted primarily in urine
and only small amounts of chromium are lost in the
hair, sweat, and bile. Therefore, urinary chromium
excretion can be used as an accurate estimation of
absorbed chromium. At normal dietary chromium
intakes (10–40 μg/day), chromium absorption is
inversely related to dietary intake. Chromium intake
is approximately 0.5% at a daily intake of 40 μg/day
and increases to 2% when the intake drops to 10 μg/
day. The inverse relationship between chromium
intake and absorption appears to be a basal control
mechanism to maintain a minimal level of absorbed
chromium. It is absorbed in the small intestine, pri-
marily in the jejunum in humans. The mechanism is
not well understood, but a nonsaturable passive dif-
fusion process seems likely. Ascorbic acid promotes
chromium absorption.
Chromium absorption in young and old subjects
is similar, but insulin-dependent diabetic patients
absorb two to four times more chromium than other
apparently healthy subjects. Diabetic subjects appear
to have an impaired ability to convert inorganic chro-
mium to a usable form. Therefore, diabetic subjects
require additional chromium and the body responds
with increased absorption, but the absorbed chro-
mium cannot be utilized effectively and is excreted in
the urine. The chromium content of tissues of these
patients is also lower.
Chromium is transported to the tissues primarily
bound to transferrin, the same protein that transports
iron. It has been hypothesized that iron interferes
with the transport of chromium in hemochromatosis
and that this may explain the high incidence of dia-
betes in hemochromatosis patients, and which may be
induced by chromium defi ciency.
Metabolic function and essentiality
Chromium in the trivalent form is an essential nutri-
ent that functions in carbohydrate, lipid, and nucleic
acid metabolism. The essentiality of chromium was
documented in 1977 when the diabetic signs and
symptoms of a patient on total parenteral nutrition
were reversed by supplemental chromium. Chromium
functions primarily through its role in the regulation
of insulin. Adequate dietary chromium leads to a nor-
malization of insulin, with reductions in blood glucose
concentration in subjects with elevated blood glucose
levels, increases in subjects with low blood glucose
levels, and no effect on subjects with near-optimal
glucose tolerance. Improved insulin function is also
associated with an improved lipid profi le. Supplemental
chromium also leads to increased insulin binding and
increased insulin receptor numbers, and recent evi-
dence suggests that chromium may be involved in
the phosphorylation and dephosphorylation of the
insulin receptor proteins.Defi ciency symptoms
The hallmark of marginal chromium defi ciency is
impaired glucose tolerance. In studies of patients
whose total parenteral nutrition solutions contained
no chromium or were supplemented with inadequate
amounts of chromium, insulin requirements were
reduced and glucose intolerance was reversed with
chromium chloride supplementation. Two of these
patients had weight loss that was restored with chro-
mium supplementation. Peripheral neuropathy was
seen in one of the patients and it too was reversed
with chromium supplementation.Toxicity
Trivalent chromium, the form of chromium found in
foods and nutrient supplements, is one of the least
toxic nutrients. The chromium often found in paints,
welding fumes, and other industrial settings is hexava-
lent and is several times more toxic than the trivalent
form. Because trivalent chromium is poorly absorbed,
high oral intakes would be necessary to attain toxic
levels. In 2001, the US Food and Nutrition Board
concluded that there are insuffi cient data to establish
a tolerable UL for trivalent chromium. However,
because of the current widespread use of chromium
supplements, more research is needed to assess
the safety of high-dose chromium intake from
supplements.Assessing status
There is no accurate method for reliable detection of
marginal chromium defi ciency. Chromium concen-
trations in hair, urine, blood, and tissues can be used