Health supplements
Article Type: Food facts From: Nutrition & Food Science, Volume 39, Issue 3.
Comment from the health supplements information service on selenium and vitamins C and E
Two studies are set to be published on-line in the Journal of the American Medical Association, which looked at selenium, vitamin E and vitamin C with reference to prostate cancer.
Commenting on the study, Dr Pamela Mason, scientific advisor to the Health Supplements Information Service (HSIS) notes: “All three nutrients investigated in these two studies – selenium, vitamin C and E are essential for human health. Dietary intake of these nutrients is very low in some groups of the population in the UK, and supplements containing selenium,vitamins C and E can help to bridge these dietary gaps and can safely be consumed in accordance with recommended dietary allowances”.
“Looking at the trials in brief, both represent the latest in a long line of studies that have attempted to use vitamins and trace elements like pharmacological agents. Vitamins and trace elements are not intended to be used like drugs. They are intended for health maintenance and for making up dietary gaps in the population. Every single officially recognised vitamin, mineral and trace element – not just two or three of them – is required to maintain health. Such studies as these two are often conducted to look at potential biochemical mechanisms for individual molecules and do not address health maintenance. All three nutrients – selenium, vitamin E and vitamin C are essential for health”.
Dr Mason continues: “Reviewing the studies more closely, the first study investigated selenium and vitamin E. 35,533 middle-aged men were randomly assigned to receive one of four interventions between August 2001 and June 2004 for a planned minimum follow-up of 7 years: selenium (200 = ECg/day);vitamin E (400 IU/day), selenium + vitamin E or placebo.
“The researchers found that there were no statistically significant differences in the absolute numbers (or 5-year incidence rates) of prostate cancer diagnoses between the four groups: placebo, 416 cases (5-year rate of 4.43 per cent); selenium, 432 cases (4.56 per cent); vitamin E, 473 cases (4.93 per cent); selenium + vitamin E, 437 cases (4.56 per cent). There were non-significant increased risks of prostate cancer in the vitamin E group and type 2 diabetes mellitus in the selenium group, but not in the selenium vitamin E group. This study has been discontinued.
“In the second study, 14,641 US male physicians age 50 years or older at the time of entering the trial, of whom 1,307 had a prior history of cancer were randomized to receive individual supplements of 400 IU of vitamin E every other day and 500mg. of vitamin C daily.
“During an average follow-up of 8.0 years, there were 1,943 confirmed total cancer cases and 1,008 prostate cancer cases. Compared with placebo,vitamin E had no real effect on the incidence of prostate cancer or total cancer. The researchers also found no significant effect of vitamin C on total cancer or prostate cancer. Neither vitamin E nor vitamin C had a significant effect on site-specific cancers, including colorectal, lung, bladder and pancreatic. Stratification by various cancer risk factors demonstrated no significant modification of the effect of vitamin E on prostate cancer risk or either agent on total cancer risk.
Dr Mason concludes: “I absolutely endorse the researcher's conclusions of the need for prudence in considering recommendations to use agents for the prevention or control of disease in the absence of convincing clinical trial results.
“In addition however, it is also imperative to reaffirm the fact that vitamins and trace elements are not intended to be used like drugs. They are essential for our daily health maintenance and for making up dietary gaps. In recent research that I undertook and authored – Towards a Healthier Britain – a substantial proportion of the UK population, young,middle-aged and old, have intakes of vitamins and minerals below reference levels. Of course, eating a healthy, balanced diet can supply all the nutrients we need, but many people continue to eat insufficient amounts of fruit,vegetables, wholegrains, dairy foods and oily fish. As a result, where there are nutrient shortfalls, a vitamin or mineral supplement will help meet that dietary shortfall”.
For more information on this report and vitamins and minerals in general log onto www.hsis.org.uk
Why are selenium, vitamins E and C essential for health?
Selenium. Selenium is a trace element, essential for health. It is found in all tissues of the body. In recommended daily amounts it has several functions:
essential for the functioning of more than 30 of the body's proteins that contain selenium (selenoproteins);
essential for the normal development, growth, metabolism of the body;
essential for normal functioning of the immune system;
helps to regulate substances that send signals between the body's cells (e.g. cytokines) which orchestrate the body's immune response;
a major antioxidant;
helps to protect cell membranes;
helps to preserve the elasticity of body tissues;
slows down the hardening (and therefore ageing) of the tissues;
functions in thyroid hormone metabolism;
helps protect the body against the toxicity of heavy metals such as cadmium, mercury and silver;
helps protect developing sperm;
plays a role in muscle metabolism; and
may help to maintain mood.
Many of the functions of selenium relate to its presence in selenoproteins. Many of the selenoproteins are antioxidants, reflecting selenium's role as a major antioxidant. For example, five of the body's glutathione peroxidase enzymes contain selenium and act as antioxidants reducing potentially damaging free radicals. Another selenium containing enzyme, thioredoxin reductase, plays a part in regenerating other antioxidants in the body and also in regulating cell growth and development. Selenoprotein P is also an antioxidant and plays a role in protecting the cells that line the inner walls of the blood cells. Selenoprotein V is found in the testes and may help in the development of sperm while selenoprotein S appears to be involved in the body's immune and inflammatory responses.
Several hormones associated with the thyroid gland are also dependent on selenium. As such, selenium influences the production of thyroid hormones. Thyroid hormones are central to the body's metabolism. Selenium therefore plays a part in the development, growth and metabolism of the body.
The UK population has a low selenium intake. The Reference Nutrient Intake(RNI) for selenium in adult men is 75 micrograms a day and for adult women is 60 micrograms a day. However, the average UK adult diet provides 39 micrograms daily, which is about half the RNI. Intakes have declined considerably during the past 25 years partly due to the use of European (rather than Canadian) wheat for bread production. Selenium enters the food chain through plants, like wheat,which take it up from the soil. The selenium content of the soil throughout much of Europe, including the UK, is low which results in selenium intakes being low.
Vitamin E
Vitamin E is a fat-soluble vitamin whose main role is as an antioxidant. It protects body cells from toxic compounds, heavy metals, such as lead and cadmium, and also from the effects of drugs, radiation and free radical damage. It works in fats and oils, which makes it complementary to vitamin C, which fights free radicals dissolved in water. Free radicals can harm cells, tissues and organs.
As an antioxidant, vitamin E helps to protect the fats in low density lipoproteins (LDLs). Lipoproteins are substances that transport fat and protein through the bloodstream. LDLs specifically transport cholesterol in the blood. If oxidised, LDLs deposit cholesterol in the blood vessels so causing build up of fat and damage to blood vessels. If LDLs are not oxidised, this helps to maintain the health of the blood vessels.
Vitamin E makes an important contribution to the health of the heart, blood and blood vessels. It helps to maintain the blood at an appropriate consistency– not too sticky – by an action on platelets, which are one type of blood cell. Vitamin E also helps in the formation of red blood cells. All of these effects help to maintain appropriate blood flow in the circulation.
Vitamin E has several functions not directly related to its antioxidant activity. Thus, it has an effect on the activity of substances such as proteins and enzymes that work in immune and inflammatory cells. This action helps to maintain the health of the body's immune and inflammatory systems.
Vitamin E also helps to regulate the activity of some of the substances in the body that send signals between cells. This is another function of vitamin E that helps to maintain the health of the body's cells.
Low and marginal intakes of vitamin E are not uncommon in the British population. There is no RNI in the UK for vitamin E but the EU Recommended Daily Amount is 10mg daily. In the National Diet and Nutrition Survey (NDNS) in British adults aged 19-64 years, 47 per cent of men overall and 67 per cent of women overall had a vitamin E intake below 10mg daily. In the 19-24 year olds,these figures increased to 60 per cent of men and 76 per cent of women.
Vitamin C
Vitamin C is a water-soluble vitamin. Like vitamin E, it is an effective antioxidant. Vitamin C can protect essential substances in the body such as proteins, lipids, carbohydrates and DNA and RNA from damage by free radicals. Vitamin C works in tandem with vitamin E and is able to regenerate vitamin E when vitamin E is used as an antioxidant.
Vitamin C is also required for the synthesis of collagen, an important structural component of blood vessels, tendons, ligaments and bone. Vitamin C plays an important role in the regulation of various neurotransmitters,including norepinephrine and acetylcholine which are critical for brain function. Vitamin C is also required for the synthesis of carnitine (http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/index.html),a substance essential for the transport of fat to the body's cells for conversion to energy. Vitamin C is also involved in the metabolism of cholesterol to bile acids (http://lpi.oregonstate.edu/infocenter/glossary.html#bileacids) and protects LDL cholesterol against damage. The vitamin is also important for the absorption of iron from plant foods (cereals, nuts, fruits,vegetables, pulses).
Evidence suggests that vitamin C plays an important role in the human immune system by protecting various types of cells, such as phagocytes, lymphocytes and neutrophils, within the immune system. As is the case for vitamin E, low intakes of vitamin C are quite common in the British population. In the NDNS in British adults, vitamin C intakes were below the RNI in 21 per cent of men and women. This increased to 25 per cent in the 19-24 year old group. In people over the age of 65, vitamin C intakes were below the RNI in 28 per cent of free living men and 36 per cent of free living women Finch et al. (1998).
It can be seen that significant dietary gaps do exist for vitamins E and C. Supplements can help to make up dietary gaps caused by poor diets, which are a problem for significant numbers of people in this country – young and old.
For more information see www.nexuspr.com
Further reading
Ball, G.F.M. (2004), Vitamin E, in Vitamins: Their Role in the Human Body, Blackwell Publishing, Oxford, pp. 234-55.
Ball, G.F.M. (2004), Vitamin C. in Vitamins: Their Role in the Human Body, Blackwell Publishing, Oxford, pp. 393-415.
Brown, K.M. and Arthur, J.R. (2001), “Selenium, selenoproteins and human health”, Public Health Nutrition, Vol. 4, pp. 593-9.
Burk, R.F., Hill, K.E. and Motley, A.K. (2003), “Selenoprotein metabolism and function evidence for more than one function of selenoprotein P”, Journal of nutrition, Vol. 133, p. 1517S20S
Finch, S., Doyle, W., Lowe, C., Bates, C., Prentice, A., Smithers, G. et al. (1998), “The National Diet and Nutrition Survey: people aged 65 years and over”, Vol. 1, Report of the Diet and Nutrition Survey,The Stationery Office, London.
Gaziano, J.M. et al. (2009), “Vitamins A and C in the prevention of prostate and total cancer in men”, JAMA, Vol. 301 No. 1, pp. 52-62, doi:10.1001/jama.2008.862
Gladyshev, V.N. (2006), “Selenoproteins and selenoproteomes”, in Hatfield D.L., Berry, M.J. and Gladyshev, V.N. (Eds), Selenium: Its Molecular Biology and Role in Human Health, 2nd ed., Springer, New York,NY, pp. 99-114.
Holben, D.H. and Smith, A.M. (1999), “The diverse role of selenium with selenoproteins: a review”, Journal of the American Dietetic Association, Vol. 99, pp. 836-43.
Kohrle, J. (2005), “Selenium and the control of thyroid hormone metabolism”, Thyroid, Vol. 15, pp. 841-53.
Ministry of Agriculture, Fisheries and Food (1997), Total Diet Study – Aluminium, Arsenic, Cadmium, Chromium, Copper, Lead, Mercury, Nickel, Selenium, Tin and Zinc (1999), MAFF, London.
Mustacich, D. and Powis, G. (2000), “Thioredoxin reductase”, The Biochemical Journal, Vol. 346, (Pt 1), pp. 1-8.
Scott, M. et al. (2009), “Effect of selenium and vitamin E on risk of prostate cancer and other cancers”, JAMA, Vol. 301 No. 1,pp. 39-51, doi:10.1001/jama.2008.864
(The) National Diet and Nutrition Survey: adults aged 19 to 64 years (2003), Vitamin and Mineral Intake and Urinary Analysis, Vol. 3, Stationery Office, London.
Traber, M.G. (2006), “Vitamin E”, in Shils, M.E., Shike, M.,Ross, A.C., Caballero, B., Cousins, R.J. (Eds), Modern Nutrition in Health and Disease, Lippincott Williams & Wilkiins, Philadelphia, PA, pp. 396-411.
Traber, M.G. (2007), “Vitamin E regulatory mechanisms”, Annual Review of Nutrition, Vol. 27, pp. 347-62.
Ursini, F., Heim, S., Kiess, M. et al. (1999), “Dual function of the selenoprotein PHGPx during sperm maturation”, Science,Vol. 285 No. 5432, pp. 1393-6.
