chromium picolinate

Sports nutrition can be infuriating. Just when you’ve think you got things sussed, along comes some new research to turn your ideas upside down. Take chromium, for example: this trace element has long been seen as vital to the integrity of carbohydrate metabolism in the body, particularly for the proper functioning of the insulin system. More recently, chromium has also found favour with athletes and coaches for its apparent ability to enhance lean muscle mass, especially when taken as a supplement in the form of chromium picolinate. However, trawl the scientific data about the benefits of chromium for athletes and things become about as clear as mud! There’s still plenty of controversy about the precise efficacy of this mineral; and to add to the confusion, the UK Food Standards Agency’s recently published report on Safe Upper Limits (SULs) in vitamin and mineral supplements proposed a ban on chromium picolinate in all chromium supplements. So what is the real story? Does chromium really work as suggested? And why has chromium picolinate been singled out as potentially harmful?

In its elemental form, pure chromium is a shiny silvery metal that was first chemically isolated from a Siberian mineral in 1797 by a French chemist called Vauquelin. Although it wasn’t realised at the time, chromium is actually widely distributed in nature, occurring in soils, water, biological materials and (to a lesser extent) even in air! However, although metallic chromium is produced on a large scale for a number of industrial purposes (for example as an additive to iron to make stainless steel), naturally occurring chromium exists almost exclusively in its ionic form as the Cr3+ ion, often known as ‘trivalent chromium’.

It was in the 1950s that nutritionists began to suspect that trivalent chromium was required by the body in order for insulin to work efficiently. However, it wasn’t until the mid-70s that chromium was firmly established as essential for human health. A study published in the American Journal of Clinical Nutrition described a female patient who had been on total parenteral nutrition (given by infusion) for over five years⁽¹⁾. As well as suffering unexplained weight loss, she also developed glucose intolerance (an inability to utilise glucose for energy), neuropathy (problems with the peripheral nerves), high levels of blood fats and abnormalities of nitrogen metabolism. The administration of insulin to improve her condition was ineffective, but when 250 micrograms per day of chromium were added to her parenteral nutrition infusate, she made a dramatic recovery. Further research confirmed these findings, and shortly afterwards the US Food and Nutrition Board designated chromium as ‘essential for human health’.

Dietary sources of chromium

Chromium is widely distributed in wholegrain breads and cereals, which typically contain around 130-140mcgs of chromium per kilo. However, the refined (white) versions of these food groups contain much lower concentrations. Meats, beans and pulses, some cheeses and spices are also quite good sources of this mineral. Fruits and vegetables are unreliable sources of chromium, while refined foods, especially those containing sugar, are very poor sources. Cooking or preparing foods using stainless steel utensils may add significant amounts of chromium to the diet. The table overleaf shows chromium contents of a number of different foods, but chromium content in different batches of the same food can vary significantly, making accurate calculations of daily chromium intake difficult to achieve.

Maintaining an optimum chromium intake can be quite difficult because there is no one exceptionally rich food source of chromium. And, to complicate matters further, some foods, particularly those rich in quick-releasing carbohydrates, can act to ‘wash out’ chromium from body stores (of which more later).

Chromium has been established relatively recently as an essential nutrient, so there is currently no UK Reference Nutrient Intake (UKRNI). However, the UK Food Standards Agency’s panel of scientific experts recently suggested a daily intake figure ‘in excess of’ 25mcg per day. Meanwhile, the US National Research Council has estimated a safe and adequate daily dietary intake at between 50 and 200mcgs for adults, which is worrying since many refined Western diets typically contain significantly less than 50mcg of dietary chromium per day.

*Figures supplied by Murray (1996)

The human body requires chromium in comparatively tiny amounts, with recommended daily intakes measured in millionths of a gram or micrograms, as opposed to the milligrams (a thousand times larger) required for most other minerals. This has made it very difficult to discover exactly how chromium is absorbed and utilised in the body. However, it seems that dietary trivalent chromium we eat in foods is passively absorbed in the gut and then binds to blood plasma proteins such as transferrin for transport around the body. Once in circulation, the main role of chromium is to enhance the action of insulin, which regulates blood sugar and is one of the body’s most anabolic hormones. Insulin acts by binding to cells and then signalling to them that the level of circulating glucose in the blood (derived mainly from digested carbohydrates) is high, thereby promoting the uptake of blood glucose by these cells. Insulin also promotes the uptake of other sugars and amino acids into cells. The overall effect of these actions is to increase the rate of glycogen and protein synthesis – hence the anabolic label.

However, simply secreting insulin into the blood isn’t enough to stimulate proper uptake of sugars and amino acids by hungry cells! Insulin, it seems, needs a little help in order to bind tightly and communicate efficiently with cells. Nutritionists have long been aware of an insulin-potentiating agent known as Glucose Tolerance Factor (GTF), which is able to help insulin to carry out its signalling role more efficiently, and recent research has identified that agent as a small peptide called chromodulin⁽²⁾. Chromodulin sits on the surface of a cell – eg a muscle cell – that is waiting to be stimulated by insulin. At this point it consists solely of amino acids, is inactive and is known as apochromodulin. But once insulin is secreted it binds circulating trivalent chromium to form a chromodulin-chromium complex, an active peptide, which stimulates the insulin receptor, enabling insulin to bind tightly and communicate with the cell. Once the insulin is properly bound to the cell, the chromodulin-chromium complex is released back into the bloodstream and is eventually excreted via the urine. If insufficient trivalent chromium is available in the circulating blood plasma, the formation of the chromodulin-chromium complex become more difficult, which in turns reduces the ability of insulin to bind and communicate properly.

When chromium is scarce in the diet, or body stores are insufficient, the benefits of increasing chromium intake are irrefutable, particularly for people with diabetes or glucose intolerance. A number of studies with such patients have demonstrated that boosting chromium intake increases insulin sensitivity, especially where body stores of the mineral are known to be low. For many people with Type II (adult-onset) diabetes, the benefits of improved chromium status, as one of a number of dietary modifications, are enough for them to dispense with insulin administration completely! But it’s not just diabetics who seem to benefit from improved chromium status. Both human⁽³⁾ and animal⁽⁴⁾ studies have shown that chromium supplementation can produce beneficial changes in blood chemistry, thereby lowering the risk of coronary heart disease (CHD). These include lower blood lipids, lower total cholesterol and increased HDL cholesterol (the protective type). Given that refined Western diets are frequently borderline or insufficient in dietary chromium, many nutritionists believe that improving the chromium status of the general population could make an important contribution to the continuing fight against CHD.

Chromium for athletes

So far so good, but where’s the evidence that extra chromium can benefit hard-training athletes, especially as exercise is known to increase chromium excretion? Can chromium really help to increase lean body mass and reduce body fat, as is often claimed by supplement manufacturers? A search of the recent literature suggests that, unless an athlete has a low or borderline chromium status, extra chromium (even when given as the popular supplement chromium picolinate) may have little or no effect on body composition. Earlier this year, a large-scale analysis of all the randomised, double-blind, placebo-controlled trials with supplemental chromium picolinate for weight loss was published⁽⁵⁾. The results show only a very small statistical effect – with most of the evidence for this derived from a single study.

Meanwhile, recent studies on chromium for strength gain are also less than convincing, with most finding little or no effect with chromium supplementation and with a lot of inconsistency, even within studies. Some researchers believe this is because chromium supplementation only benefits people whose existing chromium status is low. In other words, if you’re already getting enough chromium to meet your needs, there’s no advantage in taking more! The situation is further complicated by the fact that assessing precise chromium status is very difficult, with little correlation between chromium supply and blood plasma concentrations. Indeed, recent research suggests that impaired insulin function is associated with increased rather than reduced plasma chromium!

What about toxicity?

Various forms of trivalent chromium are used in supplements, but by far the most popular, especially among athletes, is chromium picolinate. This compound consists of a chromium atom loosely bonded to three molecules of an organic substance called picolinic acid. Studies have demonstrated that chromium picolinate is not only much better absorbed than other forms of chromium, such as chromium chloride, but also more ‘lipophilic’, which means it can accumulate more easily in cellular tissue. However, new research suggests that heavy and prolonged supplementation with chromium picolinate may have potentially harmful side effects, including the production of damaging ‘free radicals’. But, before you begin to panic, it’s important to stress that this effect has so far been observed only in test tube studies and at very high concentrations. To date there have been no animal or human studies to support these findings, so the risk remains theoretical.

Additional warnings about chromium picolinate have been issued based on individual case reports. In one of these, a 33-year-old woman, taking 1,200-2,400mcgs of chromium picolinate daily for 4-5 months in an effort to lose weight, developed renal failure⁽⁷⁾. In another, a 49-year-old woman who took 600mcgs daily for six weeks was also diagnosed with chronic renal failure⁽⁸⁾. However, these cases should be viewed in the context of more than a decade of chromium picolinate studies, in which no ill effects have been noted, and bearing in mind that this is an extremely popular supplement with the population in general, not just athletes. Nevertheless, the UK’s Food Standards Agency has called for more research on chromium picolinate and hinted at a possible future ban on over-the-counter sales meanwhile.

If you’re a regular or occasional user of chromium, or are thinking of using it as part of your nutritional strategy, where do you go from here? First, it’s important to stress that, while chromium is not a miracle muscle-enhancing or weight-loss substance, it is essential for the proper functioning of the insulin system, making it vital for any athlete to maintain an optimum chromium status. However, once this status has been attained, more is not better.

In an ideal world, we would meet all our chromium requirements from our diet. However, because of the known variability in the chromium content of foods, the increased excretion of chromium due to exercise and the difficulty in accurately determining chromium status, some routine supplementation may be the best way to maintain optimum status. Here, then, are a few guidelines for doing just that:

• Eat a wide variety of unrefined foods and ensure that your bread, cereals and pasta are of the wholemeal or wholegrain variety, which contain significantly higher amounts of dietary chromium;
• Try to minimise your consumption of quick-releasing sugary carbohydrates. Not only are these generally low in chromium, but they trigger a much stronger insulin response than complex carbohydrates, leading to greater urinary excretion of chromium via the chromodulin-chromium complex mentioned earlier;
• Regular supplementation to maintain optimum chromium status can be a useful strategy but, unless you have been clinically diagnosed with a low chromium status, you should not exceed 200mcgs per day of supplemental chromium for long periods of time;

l Although the evidence that chromium picolinate is harmful to humans at normal levels is far from solid, it may well be prudent to opt for other forms of trivalent chromium until more research data are gathered. Chromium chloride is cheap and quite well tolerated, while chromium polynicotinate (a complex of chromium and vitamin B3 molecules) is well absorbed and biologically active, albeit at a higher price!

Andrew Hamilton

References

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