Chromium

Chromium is a trace mineral needed, if at all, in microgram quantities. Sources include broccoli, wholegrains, meat, nuts and brewer's yeast, though content varies widely and is affected by processing and even by the equipment food is prepared with.

Its status is unusual among minerals in this index. Chromium was long classed as essential, but that classification has been questioned, since no clear deficiency state has been demonstrated in otherwise healthy people. Some authorities have moved away from setting a reference intake for it at all.

Chromium picolinate is the most common supplemental form and the one used in most research. Trivalent chromium is the form found in food and supplements; the hexavalent form is an industrial contaminant and an entirely different and hazardous substance, which is worth being clear about since the names look similar.

The proposed mechanism is that chromium supports insulin signalling, improving how effectively cells respond to insulin and take up glucose.

This was originally attributed to a compound called glucose tolerance factor, and later to a chromium-binding molecule sometimes called chromodulin. The details of how, or whether, this operates in humans remain unsettled.

The appetite and craving claims derive from the same proposed insulin effects, on the reasoning that steadier blood sugar means fewer cravings. That is a plausible chain of logic rather than a demonstrated one, and it is a long way from mechanism to outcome.

Meta-analyses of chromium supplementation for blood sugar markers have produced mixed results, with any effects generally small and inconsistent, and clearer in people whose markers were abnormal to begin with than in healthy people.

For body weight and body composition, the evidence is weak. Reviews have generally found effects that are statistically detectable but too small to be meaningful in practice, on the order of a kilogram or less over several months.

The craving and appetite claims that drive most sales rest on a small number of studies and have not been robustly replicated. Chromium is one of the clearer cases in this index of a supplement whose market presence considerably exceeds its evidence.

Trivalent chromium from food and supplements is generally well tolerated, and absorption is low enough that most of an oral dose is not taken up at all.

Occasional reports include headache, digestive upset and mood changes. There have been isolated case reports of problems at very high long-term doses, mostly involving intakes far above what supplements provide.

Because chromium may affect blood sugar, take care if yours is being managed, and speak to your doctor before use if you take regular medication.