Anatomy and physiology

Possible protection against cancer and improved immune function make supplementation with selenium attractive, but its toxicity and other unknown effects urge caution Selenium presents a nutritional conundrum because of its dual status as a highly toxic, but essential, trace element.1 The eightfold gap between the estimated average requirement2 and the upper limit of safe intake is relatively narrow, so questions of too much and too little are important. Additional key questions pertain to adequate versus optimal status, and reflect the shift in focus of nutrition from preventing deficiency towards promoting optimal health. As is the case for many micronutrients, the quest for protective effects of selenium (Se) intakes above requirements is rapidly gaining momentum. Ever since the biological role of Se in humans was first delineated less than 30 years ago, evidence for its increasing scope and importance to human health has been rapidly accumulating. Increasingly, Se depletion, as opposed to “deficiency”, is being associated with a range of health outcomes, including viral infection, reproduction, mood, thyroid function, cardiovascular disease, inflammatory conditions, immune function and cancer protection. 3,4 It is possible to advance a range of theoretical arguments that suboptimal Se status may have an effect on health, but evidence of a direct relationship to health outcomes is very limited. Se research is incipient and there is a paucity of data. For example, Se reference values that have been adopted in the United States2 are based on only two studies, one of which was a 1983 Chinese study of poor quality. Research is hampered by substantial difficulties in assessing and interpreting Se intakes and status, which become even more significant in the context of extreme global variations in the Se content of soil, food and human tissue.3,4 We do know that Se has key roles in redox regulation and antioxidant function, and hence in membrane integrity, energy metabolism and protection against DNA damage. 1,3,4 These and other functions are mediated through over 35 selenoproteins, which require adequate Se intake for synthesis and expression. Selenoproteins include several forms of the enzymes glutathione peroxidase (GPx), thioredoxin reductase and iodothyronine 5'-deiodinase. The number of known selenoproteins has almost trebled over the past 7 years,1,3 although the roles of several remain undefined. Plasma Se concentration is the most commonly used indicator of Se status.2 Low Se intakes, plasma Se concentrations and GPx activities have direct, linear associations up to a threshold plasma Se concentration (70–100 μg/L), beyond which GPx activity plateaus. This maximum GPx concentration is thought to represent repletion, and commensurate Se intake forms the basis of recommended dietary requirements.2,5 Concentrations of other selenoproteins are also influenced by Se intake and may have a role as functional indicators of Se status, 2,3,5 but assay methods and reference standards are at an early stage, and comparisons between studies are difficult. There is differential hierarchical expression of the selenoproteins, with relative preservation of the presumably more metabolically important at lower intakes of Se. 1,3 However, we do not clearly understand the health implications of submaximal expression of the selenoproteins. There are enormous geographical variations in the Se content of soil and food, and hence in Se intakes and concentrations in human blood and tissues.3,4,6 Thus, it is essential to use local data for monitoring and interpreting Se status.6 The 2000 US Recommended Dietary Allowance (RDA) is 55 μg/day.2 The 1987 Australian RDAs are 70 μg/day for women and 85 μg/day for men, but these are currently under review.7 Organic selenomethionine is the predominant form of Se in food. The most important dietary sources of Se are meat, poultry, fish and cereals (although brazil nuts are very high in Se and certain fish also have particularly high levels). Accurate assessment of intake is exceptionally difficult because the Se content of food is so variable. 2,3,6,8 Estimates of Se intakes include 106 μg/day in a large representative US sample,2 and a range of 29–70 μg/day in Europe.3 Extremely limited Australian data suggest intakes of around 90 μg/day,6 while more comprehensive New Zealand data show intakes as low as 28 μg/day, and indicate that conventional dietary intake methods are inadequate for estimating Se intake.8 Inorganic Se (selenite and selenate) is only available through supplementation, is generally less bioavailable and produces a different physiological response than organic forms of Se. 1,2 Environmental changes and agricultural practices may be reducing Se concentrations in soil.4 These factors, in conjunction with trade barriers (eg, the cessation of importing high-Se US wheat to the European Union), appear to be associated with a decline in the availability of Se through the food chain and in human Se status, particularly in Europe.3 Changes in food supply and habits, including the importation of Australian wheat, have improved the previously marginal Se status of New Zealanders.9 Twenty-six European studies since 1990 all reported mean plasma Se concentrations below 100 μg/L, the level postulated to be required for GPx saturation and cancer protection. 3,10 Ten of these studies reported plasma Se levels under 70 μg/L,3 postulated by others to be associated with GPx saturation.11 A representative US plasma Se level was 124 μg/L.2 In this issue of the Journal (page 383), Lyons and colleagues present evidence that although mean plasma Se concentrations of South Australians are relatively high by European standards, they may be declining, and over a third of their sample had levels below 100 μg/L.12 Overt human Se deficiency is rare. It is manifested as Keshan disease, an endemic fatal cardiomyopathy, which is virtually unknown outside areas of China, where the levels of Se in soil and dietary Se intake are extremely low. A few studies have reported Se deficiency as a result of long-term total parenteral nutrition.1 Despite myriad claims for potential relationships between a range of diseases and Se status, there are no clear population health outcomes that can be attributed to Se status in countries like New Zealand, where intakes are very low. 1,9 The evidence for an effect of Se on health outcomes is strongest in cancer prevention. Secondary findings from the 10-year US Nutritional Prevention of Cancer Trial demonstrated a protective effect of supplementation with 200 μg/day of organic Se (from yeast) on total cancer incidence and mortality, and on prostrate cancer incidence (relative risk, 0.75, 0.59, and 0.48, respectively).10 The effects were stronger in men and in those with lower baseline plasma Se levels (< 105 μg/L), and were not found for a range of other site-specific cancers. Of concern is that in the top tertile for baseline plasma Se level there may be an association between supplementation and increased risk of breast cancer and melanoma, as well as overall cancer incidence.10 There are numerous limitations to what was a small study, and the relatively high baseline plasma Se levels (114 μg/L) make it difficult to generalise the findings. It appears that protection from cancer may require supplementation beyond correction of depletion and maximal expression of the selenoproteins. Several large trials are under way to clarify the benefits and risks of Se supplementation with respect to tumorigenesis. More speculative and tantalising is the potential association between Se and immune function. Evidence suggests that reduced Se status may be associated with the incidence of clinical infection in adults,13 and supplementation of apparently Se-replete individuals potentially enhances immune function.3 Animal studies indicate that the Se status of the host can genetically alter invading viral pathogens, so that a normally benign strain may become virulent in an Se-deficient host.14 This is of interest given the emergence of new influenza virus strains from China, where there are significant areas of overt Se deficiency, and given the decline in Se status associated with progression of HIV infection.3 In summary, there has been an explosion of interest in the biological role of Se and the potential health implications of Se status. Much of the evidence in humans is descriptive, and the dearth of quality prospective trials means the links with many diseases are still controversial and, in many cases, speculative. There are very limited representative data on Se content of the food supply and Se status in many populous parts of the world, and no nationally representative Australian data. Lyons and colleagues provide the most comprehensive Australian plasma Se data to date,12 but they are neither prospective nor representative, and there may be variations according to states.6 Outcomes of research on Se in the next decade are likely to be important, and we urgently need more Australian data. Meanwhile, it is necessary to remember that selenium is toxic.1-3 Intakes below 400 μg/day are considered safe for almost all individuals.2 As illustrated by the Nutritional Prevention of Cancer Trial,10 outcomes of Se supplementation are variable and may not be without risk. Benefits and an appropriate dose for supplementation remain controversial. Until further evidence is available, supplementation should be recommended with caution, and overconsumption should be avoided.3

Lynne A Daniels PhD, APD

Objective: To assess trends in selenium status in South Australians from 1977 to 2002.Design: Six cross-sectional surveys.Participants: 117 participants in 1977, 30 in 1979, 96 and 103 (separate surveys) in 1987, 200 in 1988, and 288 volunteer blood donors in 2002. A total of 834 healthy Australian adults (mean age, 42 years [range, 17–71 years]; 445 were male).Main outcome measures: Plasma and whole blood selenium concentrations.Results: The 2002 survey yielded a mean plasma selenium concentration of 103 μg/L (SE, 0.65), which reached the estimated nutritional adequacy level of 100 μg/L plasma selenium. Mean whole blood selenium declined 20% from the 1977 and 1979 surveys (mean whole blood selenium concentration, 153 μg/L) to the 1987, 1988 and 2002 surveys (mean whole blood selenium concentration, 122 μg/L). Plasma selenium was higher in men (P = 0.01), and increased with age in both men and women (P = 0.008).Conclusions: In healthy South Australian adults sampled from 1977 to 2002, whole blood and plasma selenium concentrations were above those reported for most other countries and in most previous Australian studies, notwithstanding an apparent decline in selenium status from the late 1970s to the late 1980s.

Graham H Lyons BAgricSc, MPH · James C R Stangoulis BAgricSc, PhD · Lyndon T Palmer BSc · Robin D Graham PhD, DAgricSc · Geoffrey J Judson BRurSc, PhD · Janine A Jones BCom/Eco, MStatSocAust

Shanthi Kannan,* Christine H Rowland,† Gregory I Hockings,† Peta M Tauchmann,‡ Edwin A Blackwell§ * Endocrine Advanced Trainee, † Endocrinologist, ‡ Nurse Educator, § Haematologist, Greenslopes Private Hospital, Brisbane, QLD. Correspondence: Dr Christine Rowland, Greenslopes Private Hospital, Newdegate Street, Greenslopes, Brisbane, QLD 4120. c.rowlandATmailbox.uq.edu.au To the Editor: Intravenous immunoglobulin preparations containing maltose (eg, Intragam P [CSL Limited]) can interfere with the readings of blood glucose monitors that use test strips with glucose dehydrogenase, such as Advantage (Roche).1 Glucose dehydrogenase is an enzyme of the Pyrroloquinolinequinone class which reacts with the disaccharide isomer maltose present in Intragam P at concentrations of 10 g/100 mL,2 resulting in falsely elevated blood glucose level results. Blood glucose monitors, such as Precision (Medisense products), Medisense (Medisense products)3 or Accutrend (Roche), that use the glucose oxidase system, do not react with maltose and can be safely used for patients receiving Intragam P. We have had two patients in whom capillary blood glucose levels were over-estimated. One was a 64-year-old woman with type 2 diabetes who was being treated with haemodialysis, and who received Intragam P for immune-mediated thrombocytopenic purpura. Before being admitted, her diabetes was reasonably controlled by 10 units of protophane twice daily. She received prednisone (100 mg/day) from Day 1 to Day 13 and Intragam P intravenously each day from Day 2 to Day 6 and from Day 14 to Day 18. While the patient was receiving Intragam P, the Advantage monitor gave persistently higher readings than both the Precision monitor and plasma glucose level measurements. The following paired readings were obtained: Advantage capillary glucose reading of 9.3 mmol/L while the plasma glucose level was 2.3 mmol/L; and Advantage capillary glucose reading of 24.4 mmol/L while the plasma glucose level was 10.4 mmol/L. During the second course of Intragam P we noted that readings with the Precision monitor were equivalent to the measured plasma glucose level. This patient developed hypoglycaemia because her insulin doses were increased on the basis of falsely elevated capillary glucose readings as measured on Advantage blood glucose strips. A Precision monitor was used for this patient until after the haemodialysis treatment which followed the final dose of Intragam P. After this time Advantage blood glucose readings approached those obtained with the Precision monitor. A second patient — a 35-year-old woman who was not known to have diabetes, but was having her glucose levels monitored while undergoing total parenteral nutrition — was given Intragam P for idiopathic thrombocytopenic purpura. While receiving Intragam P, capillary glucose levels by the Advantage monitor were elevated by 13–20 mmol/L compared with concurrent (and normal) plasma glucose level measurements. It has previously been reported that icodextrin, used in some peritoneal dialysis fluids, can have similar effects, as it is hydrolysed to oligosaccharides, including maltose, maltotriose and maltotetraose.4,5 The reaction with maltose has important clinical implications. Although it is stated in the product information for Advantage test strips that glucose readings may be affected by maltose levels over 16 mg/dL (0.89 mmol/L), clinicians may not be aware that Intragam P is in a maltose solution. For patients receiving Intragam P, the Advantage monitor is not suitable, and the Precision, Medisense or Accutrend blood glucose monitors, which use glucose oxidase which does not react with maltose, should be used instead. We have reported our experience to the Australian Red Cross Blood Service as an adverse event.

Shanthi Kannan · Christine H Rowland · Gregory I Hockings · Peta M Tauchmann · Edwin A Blackwell

Tissue engineering involves the use of cells (either adult, mesenchymal or embryonic stem cells) coupled with biological or artificial matrices or scaffolds which guide the cells during repair or regeneration of the tissue. Recently discovered and isolated growth factors can promote either adult or stem-cell growth and differentiation along selected pathways to re-form and repair skeletal tissues in adults. Bone repair enhancement and ...

Barry W Oakes MB BS, MD

To the Editor: Preparations containing isoflavone phytoestrogens are widely used as an alternative therapy for treating symptoms of the menopause. Although Australian government regulations strictly control the components of alternative therapies, adherence to the stated amounts of the components in alternative therapies is not routinely assessed. Isoflavones exist in two forms — aglycone (the free form) and glycosylated or glycone (the conjugated form) — the relative proportions of which vary between preparations. As glycosylation contributes considerably to the mass of isoflavone molecules, it is relevant to consider the total amount of potentially available isoflavone in alternative therapy preparations. Isoflavone-containing preparations which had a recommended daily dose on their labels were purchased at random from pharmacies around Sydney during September 1999. Where possible, products from more than one manufacturing batch were purchased and all products were well within their stated shelf life. The tablets, capsules or powder were removed from their packaging to conceal their identity and randomly allocated to numbered plastic bags by the hospital pharmacy department. The samples were then sent to PhytoChem Technologies Inc (Chelmsford, Mass, USA), an independent reference laboratory for the assay of isoflavones. There, isoflavones were extracted within four months of purchase (and before their stated use-by date) from 500 mg of each specimen after dissolution in 70% methanol. Glycosylated and free isoflavones were assayed in duplicate by gradient high-pressure liquid chromatography, with detection of isoflavones at 254 nm using a Waters 996 series photodiode detector with a limit of detection of 0.2 µg/mL. The identity of chromatogram peaks was confirmed by UV–V spectral analysis, and by comparison with standards. The mobile phase was acetonitrile, and adequate peak separation, linearity, accuracy and reproducibility were demonstrated. The total amount of available aglycone isoflavones in each sample was estimated (see Table). Only two products (Phytolife and Promensil) had total isoflavone contents close to the stated amount, and the content of the Phytolife product was variable. Estimated aglycone contents of preparations demonstrated that glycosylated isoflavones contributed substantially to the stated content of the product. A previous study of isoflavone-containing preparations marketed in the United States produced similar results to ours.1 Consumers may wish to consider not only whether an alternative therapy is of use, but also whether the product they purchase contains what they expect. Actual and stated isoflavone content of commercially available preparations Manufacturer Product No. of batches assayed Stated isoflavone content (mg) in recommended daily maximum dose of product Actual total isoflavone content per daily dose (mg) Estimated aglycone isoflavone content per daily dose (mg) Blackmores Phytolife one a day 5 40 41.02 ± 6.12 25.75 ± 6.04 Bioglan Soy powder plus 4 68 48.75 ± 1.42 30.44 ± 0.86 Earths Own Soy + calcium 1 68 42.52 25.67 Health Direction Femme phase 1 235 mg soy protein* 0.29 0.20 Herron Phyto source 1 22.5 16.27 9.93 Natural Nutrition Menopause 1 60 0.56 0.51 Natural Nutrition Phytobalance 3 90 58.12 ± 6.26 34.96 ± 3.79 Novogen Promensil 4 40 40.12 ± 1.98 38.38 ± 1.20 Pretorius Maxi soy plus red clover wild yam and calcium 4 68 50.36 ± 1.64 31.24 ± 1.13 Wagner Probiotics Femme soy plus with red clover 2 27 30.76 ± 0.12 19.65 ± 0.05 * Soy protein has a high isoflavone content. Values are the mean ± standard deviation. Total isoflavones = glycone plus aglycone. Estimated available aglycone isoflavones = weight of aglycone isoflavones plus weight of glycone isoflavones corrected for glycone content.

Jan B Howes · Laurence G Howes

The Research Enterprise Funding Australia's basic biomedical research of 1993 and 1994 The meshing of two databases of scientific publications -- the Wellcome Trust's Research Outputs Database, and the Research Evaluation and Policy Project's database of Australian publications -- allows a detailed analysis of the funding agencies providing external (as opposed to intramural) support for Australia's basic biomedical research. This analysis shows the success Australian researchers are having in attracting funding from overseas, and the high citation rates achieved by publications with external funding. Linda Butler MJA 1999; 171: 629-633 Introduction - Characteristics of basic biomedical research funding - Comparison of funded and unfunded publications - The impact of funded research - Conclusions - References - Authors' details - - More articles on Economics

Linda Butler