Chromium is an essential trace mineral that is found in some foods, but is also taken by some people as a supplement. Foods that are good sources of chromium include liver, kidney, yeast products, wholegrain cereal, nuts and legumes. Most people get enough chromium from food.Chromium is involved in making glucose available for energy, which is why it has been studied to see if it would be helpful in managing diabetes. However, Diabetes UK says there is no clinical evidence yet to support chromium for people with diabetes. For a supplement to be sold making claims about being beneficial to aspects of a person's health, claims have to be approved by the European food regulator EFSA. It has approved a health claim that chromium contributes to the maintenance of normal blood glucose levels.Health claims that chromium helps with body weight management or reducing fatigue or tiredness have not been approved.Some studies have also found that chromium may help with polycystic ovary syndrome (PCOS), which is linked to insulin resistance.
In a pilot study published in the US journal Fertility and Sterility, researchers at the State University of New York, analysed the effects of nutritional supplementation with chromium on six women with PCOS. Results showed that daily supplements of 1,000 mcg of chromium significantly enhanced insulin sensitivity. However, this was a small trial and larger controlled trials are needed to confirm efficacy.Chromium supplements have also been studied for their effects on cholesterol, heart disease risk, psychological disorders, Parkinson’s disease and other conditions. However, the study results have been contradictory or unclear.Some people use chromium supplements to build muscle or trigger weight loss. Again, results have been inconclusive and more research is needed.For labelling purposes, the European Union’s Recommended Daily Allowance (EU RDA) for chromium has been set at 40mcg per day for adults.Many people get more chromium than that. However, no one knows exactly how much more is safe.
The UK Expert Group on Vitamins and Minerals report on safe upper limits suggests that intakes of chromium of up to 10mg (10,000mcg) per person per day would be expected to be without adverse health effects. Excessive doses of chromium may actually worsen insulin sensitivity.Chromium - specifically trivalent chromium - usually comes in capsules and tablets. It’s also sold in many different formulas with different names. The most commonly used is chromium picolinate. Others include chromium chloride and chromium nicotinate. Another form of chromium not found in foods or supplements - called hexavalent chromium - is used in some industries. It is highly toxic.Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.Selenium is an essential mineral and micronutrient. It is fundamental to human health and found in many foods.
It is found in meat, grain cereals, egg yolk, milk, brazil nuts, mushrooms, garlic and seafood (hence, selenium levels are high in populations with high intake of seafood, like the Inuit population).Selenoproteins are important constituents of a number of enzymes with a range of functions including antioxidant function, thyroid hormone metabolism, male fertility and immune mechanisms. A decline in blood selenium levels in the UK and other European countries has raised concern about possible public health implications, particularly in relation to cancer and cardiovascular disease. Whilst there is some understanding of the role of these proteins in health and disease (and some interesting theories and research), there are many unanswered questions and much debate about supplementation. More research is repeatedly called for.[2] Deficiency is linked with a wide variety of medical problems but excessive intake can have toxic effects and may even be carcinogenic.Dietary recommendations for selenium differ between countries.
This is because there is uncertainty over what constitutes 'optimal selenium status'.[4] The average daily intake of selenium in in the UK has been falling over a 30-year period. In the UK, the recommended daily allowance (RDA) is 75 micrograms/day for men and 60 micrograms/day for women.In the USA, the RDA is 55 micrograms/day for adults. The World Health Organization (WHO) RDA for selenium is 70 micrograms/day to 350 micrograms/day. Some are recommending supranutritional supplements of 200 micrograms/day to 800 micrograms/day. Toxic effects probably occur at around 40x the RDA.Erythrocyte, serum and tissue levels of glutathione peroxidase (GP) can be measured to assess selenium status.Selenium in hair and nails can also be measured. Discuss with your laboratory before deciding which method to use.Dietary recommendations were made over 20 years ago on the basis of blood levels of GP. This intracellular enzyme converts hydroxyl radicals or hydrogen peroxide into water and this requires selenium as a co-factor.
Levels of this enzyme have thus been taken to correlate with selenium levels. Since then, over 30 new selenoproteins have been identified and about half of these have an identified biological function.These selenoproteins include:Four GP enzymes, a major class of functionally important selenoproteins and the first to be characterised:Classical GP x 1.Gastrointestinal GP x 2.Plasma GP x 3.Phospholipid hydroperoxide GP x 4.Thioredoxin reductase (TR), a selenocysteine-containing enzyme important in regulating metabolic activity.Selenoprotein P (60% of plasma selenium is held in this form) may have a role in the transport of selenium but also may have other functions.Several iodothyronine deiodinase enzymes. These are responsible for conversion of the prohormone thyroxine to the active thyroid hormones (triiodothyronine, or T3).Sperm capsule selenoprotein which may be responsible for maintaining integrity of the sperm flagella (and hence motility of sperm).This is involved in muscle metabolism.
Deficiency of selenium may cause a variety of problems but the health implications of a decline in selenium levels in the UK over 25 years have not been systematically investigated. In general, selenium is thought to be important in a number of varied aspects of health: for a healthy immune system, for a protective effect against some forms of cancer, to maintain and enhance male fertility, for a reduction in cardiovascular mortality and to regulate inflammatory markers in asthma. Research is in progress and there is a lot of interest in the results of this research. Although there are still many unanswered questions, so far selenium has been linked with:Counteracting the development of virulence and inhibiting HIV progression to AIDS.[9]22Trials are small and results mixed but more research is called for.A possible role in preventing pre-eclampsia.A possible relationship between mood disturbance and selenium deficiency.A possible association between elevated selenium intake and reduced cancer risk.
The association between selenium status and cancer risk remains enigmatic and epidemiological studies have failed to consistently link low selenium levels with increased cancer risk in men and women.[14] It is possible that there may be gender differences in susceptibility to cancer risk with men being more susceptible to the risk of low selenium. In the Nutritional Prevention of Cancer Trial, daily supplementation of selenium significantly reduced prostate cancer in men.[15] It is thought that the greatest benefit from selenium supplementation will be in low selenium status populations, although the biggest primary and secondary prevention trials - SELECT (= Selenium and Vitamin E Cancer Prevention Trials) - were carried out in the USA where selenium status is good.[16] Some were predicting that the SELECT results in 2013 would show benefit.[17] However, the trial was discontinued because there was no evidence of a benefit from either vitamin E or selenium on prevention of prostate cancer.
[18] Concern was also raised about a link between selenium supplementation and an increased risk of developing type 2 diabetes.In asthma, some epidemiological studies suggest that deficiencies of selenium, zinc and other nutrients (vitamins A, C, D and E) may be associated with the development of allergic disorders and asthma.[20] Although a number of trials suggest supplementation with selenium may help symptoms of chronic asthma, only one small trial, according to the Cochrane review, showed evidence of this.The hypotheses that low selenium concentrations are associated with increased cardiovascular disease and that selenium supplements prevent coronary heart disease are unproven. Selenium supplementation cannot currently be recommended for cardiovascular disease prevention.[23] Deficiency is associated with cardiomyopathy in general, but particularly in Keshan disease, a congestive cardiomyopathy associated with Coxsackievirus and selenium deficiency.Deficiency in trauma and burns patients.
One study reports improved recovery with selenium supplementation in trauma and burns patients.The thyroid gland contains more selenium than any other tissue. Selenium deficiency may help to precipitate hypothyroidism and autoimmune thyroid disease and supplementation may contribute to prevention of these diseases.Risk factors include:Poor dietary intake. Because selenium is found in meat and seafood, vegetarians in areas with low environmental selenium may become deficient.Lower levels have been found in people receiving state benefits or with lower educational attainment.The elderly living in residential or nursing homes had lower levels of selenium when compared with 'free-living' elderly patients.The elderly, particularly in areas where low intake is common.Where you live:Areas with a low selenium soil environment are associated with deficiency. The elderly in such areas are particularly at risk and one study from New Zealand demonstrated suboptimal levels of selenium in a significant proportion of 103 elderly New Zealand women.
The levels of selenium are higher in the south of England than in the north.[28] The selenium status may vary within countries according to factors such as the selenium in the local soil but is also affected by the levels of selenium in imported crops.Patients on total parenteral nutrition (TPN).Trauma and burns patients.Those at high risk of deficiency should have their selenium status measured. If deficient in selenium, such patients should certainly be given supplements. As with many nutritional components, distinction must be drawn between the basic nutritional requirement to prevent deficiency and supplementation to prevent, for example, chronic disease and cancer.According to a report from the USA, 99% of over 17,000 subjects were 'selenium replete' according to plasma selenium levels and not in need of routine supplementation.[35] There is widespread questioning of the use of RDAs and some questioning of methods of assessing deficiency in this as in other areas of nutrition.Evidence of benefit at supranutritional levels of dietary intake is needed to support what has been called the 'nutraceutical' approach to supplementation.