CHROMIUM

Chemistry

Transition metal; multiple valence states. Most Cr in food or water is Cr (III). Cr (IV) – chromate or dichromate – is a strong oxidising agent. In small amounts contaminating food or water, Cr (IV) is reduced to (III) in the acidic environment of the stomach.

History

• 1959: Cr deficiency observed in rats; Cr-poor diet led to increased glucose level in blood.
• Undernourished children responded to chromium supplement; treatment improved glucose tolerance.
• 1977: 3 patients on long-term intravenous nutrition (Total Parenteral Nutrition, TPN): clinical deficiency described - hyperglycemia, weight loss.

• Presently, chromium supplements are sold as a slimming aid and muscle building preparation. Any evidence?

Functions

The function of chromium as an essential nutrient remains unclear.

It may form a ’glucose tolerance factor’ in association with nicotinic acid and gly, cyc and glu. But the complex has not been purified.

Cr potentiates the action of insulin in vivo and in vitro. Cr has beneficial effects on blood lipid profiles (cholesterol, LDL and triglycerides are decreased; HDL and apolipoprotein A levels increased).

Absorption and homeostasis

(Difficult to investigate, because of low levels in tissues and in food, and high risk of contamination.)

• Poorly absorbed: probably <2% of intake. Hindered by fibre (phytic acid?) Fe? Zn? Assisted by vitamin C, oxalate?
• Transported by transferrin.
• Highest concentration in bone, spleen, liver and kidneys.
• Excreted in faeces

Criticisms

Some experts (notably Finnish researchers) are sceptical about the identification of Cr as an essential trace element for humans, in view of the sparse evidence available.