Hunger and malnutrition

Transcription

1 UNCOVERING THE HIDDEN LINKS NUCLEAR & ISOTOPE TECHNIQUES TARGET NUTRITIONAL NEEDS BY VENKATESH IYENGAR Hunger and manutrition are among the most devastating probems facing the majority of the word s poor and needy. Severa United Nations Conferences on Food and Nutrition have highighted the need for eiminating poverty and manutrition, especiay among women and chidren. Nucear and isotopic techniques are vauabe toos in heping to meet the mutifaceted chaenges. Each year 30 miion infants in the deveoping word are born with intra-uterine grow t h re t a rdation eading to ow weight at birth. This re p re s e n t s about 24% of the births in these countries. Neary 200 miion chidren (more than 150 miion in Asia and about 27 miion in Africa) under age f i ve are moderatey to seve re y undernourished, whie 70 miion are seve re y undernourished. T h e re are p rojections that about one biion chidren wi be g rowing up by 2020 with i m p a i red menta deve o p m e n t. Aduts suffer as we. About 243 miion aduts in deveoping countries are reportedy undernourished, which owers their work capacity and resistance to infection. Anemia in mothers is pandemic, surpassing 80% in some countries, and is associated with very high rates of materna mortaity. Evidence from both deveoping and industriaized countries inks materna and eary chidhood manutrition to increased susceptibiity in adut ife to diabetes, heart disease, and hypertension. A fundamenta ink is emerging between mother and chid manutrition and the chid s subsequent marked sensitivity to abdomina obesity, diabetes, high bood pressure, and coronary heart disease. Added to this is the burden of over-nutrition and obesity that is rapidy emerging in the same deveoping countries, affecting chidren and aduts aike. Since the eary 1990s, emerging probems of what is caed hidden or sient h u n g e r have commanded g reater attention. The term refers to micro n u t r i e n t manutrition found in men, women, and chidren who are persistenty undernourished. Ac c o rding to goba estimates, some 2 biion peope in more than 100 deveoping countries suffer from mutipe m i c ronutrient deficiencies. Mo re than 90% of pre g n a n t women and pre s c h o o c h i d ren in deve o p i n g countries show signs of iro n deficiency anemia and other reated disord e r s. Nutritiona Disorders Across the Human Lifespan. Manutrition seriousy affects individuas in a stages of human ife. Combating nutrition-reated disorders that span across the entire ife cyce wi be the biggest task for scientists in the decades ahead. (See tabe, page 18.) Manutrition during pregnancy often resuts in intrauterine growth retardation (IUGR) of the fetus, resuting in ow birth weight of the infant. This directy infuences the surviva and growth of young chidren. Poor nutritiona status of the mother during actation further compounds the aready existing negative effects on the growing infant. These undernourished chidren in ater years show poor performance at schoo. Adoescent nutrition is an area that is just being recognized as one that requires nutritiona monitoring. Mr Iyengar is Head of the IAEA Section on Nutrition and Heath Reated Environmenta Studies, Department of Nucear Sciences and Appications. Fu references are avaiabe from the author at V.Iyengar@iaea.org 15

2 16 Chidren gain up to 50% of their adut weight, 20% of their adut height, and 50% of their adut skeeta mass during this crucia stage of adoescent ife. Energy, protein, cacium and micronutrients, incuding iron, zinc and foate, are required at maximum eves. Deficits in intake of nutrients coud signa the start of nutrition-reated disorders in aduthood. Manourished aduts have decreased overa resistance to disease and increased disabiity at work, eventuay affecting the overa quaity of ife, especiay as they join the ranks of the edery. Nutrition of the edery is of specia concern because of the high pre vaence of o s t e o p o rosis. This serious disease is characterized by ow bone density and eads to f r a c t u res (particuary in postmenopausa women), s e ve rey imiting their quaity of ife. Aging is aso associated with changes in body composition, such as a decine in ean body mass, and with an i n c rease in the risks of disease and accidents. T h u s, i n c reasing attention to nutritiona needs and care of the aged is important to reduce the risk of the onset of o s t e o p o rosis and other d e g e n e r a t i ve diseases. Poution Interactions & Reated Diseases. The severity of manutrition is further exacerbated by environmenta poution. Poutants such as ead and oxides of nitrogen have debiitating effects on peope who are aready poory nourished. Poution, in the arger context, encompasses both anthropogenic and nonanthropogenic factors. Parasitic infestations, and the spread of infections through communicabe diseases, form a major segment of the environmenta component of nutritiona disease. In Asia, Africa, and Latin America, the manourished popuations suffer from a host of other nutrient deficiencies and are more prone to parasitic infestations (hookworm, amoebiasis) and maaria. The contrast in mortaity between peope iving in deveoped and deveoping countries, arising out of the differentia oad of infections, is a key indicator. (See graph, page 17.) Operating in synergism with diarrhea, respiratory and other infections, poor diets in eary chidhood ead to growth faiure, deayed motor and menta deveopment, impaired immunocompetence, and higher risks of compications and deaths from infectious disease. Another critica issue is food s a f e t y, which touches seve r a aspects surrounding the n u t r i t i o n - h e a t h - d i s e a s e domain. The study of nutritiona toxicoogy is fast becoming a goba chaenge. Inter-eement interactions of ead and iron (anemia), m e rc u ry and iron, arsenic and seenium, seenium and iodine, cadmium and zinc, are becoming an area of concern. So is pacenta transfer of nutrients and toxicants fro m the mother to the fetus. C h i d ren are more susceptibe to the effects of ead and a combination of iron deficiency and ead toxicity in them can h a ve devastating effects. Hi g h e r e ves of ead may be absorbed in chidren with iron deficiency anemia compared to those who are iron sufficient. Besides heavy metas, nutrient interactions with pesticides, oxides of nitrogen, tobacco, and acoho are important to understand. The combination of poution and manutrition affects an individua s quaity of ife, causing disabiity and morbidity. This is often expressed as Disabiity- Adjusted Life Years (DALY), which is a composite measure of the time ost due to premature mortaity and time ived with disabiity. The higher the magnitude of the DALYs, the greater the burden of disease. A significant fraction of the DALYs wordwide is contributed by infectious and parasitic diseases. On a regiona basis, over 40% DALY due to infectious and parasitic disease is seen in sub-saharan Africa as opposed to ess than 3% in the European region. RESPONDING TO THE NEEDS Goba nutrition probems raise a host of questions and warrant action by the internationa community of scientists, nutritionists, physicians and other medica professionas. What steps shoud be taken to remedy this situation? How can this be accompished economicay? How can progress be monitored? What is the roe of technoogy in the overa monitoring process? The ast question, which is most reevant to this artice, is of particuar importance to the IAEA and its support of nutrition programmes. The IAEA s activities in human nutrition were initiated to appy nucear and reated

3 isotopic techniques for soving probems prevaent in deveoping countries. Among the numerous appications avaiabe, isotopic techniques are uniquey we suited to targeting and tracking progress in food and nutrition deveopment programmes. These are toos that hep evauate nutritiona status of individuas and popuations, measure nutrient requirements and the uptake and bioavaiabiity of vitamins and mineras. The IAEA s efforts hep to: n verify the nature of the nutrition probem and the efficacy of specific interventions; n impement nutrition intervention programmes by monitoring effectiveness and reducing programme costs; n guide in the processing of oca foods for optima nutritiona vaue; n serve as eary indicators of important ong-term heath improvements; and n strengthen capacity buiding in deveoping countries. Heath and nutrition monitoring has been strengthened through extensive nucear and isotope appications in industriaized countries to anayze human energy requirements, body composition, and the metaboism of important nutrients such as protein, fat, vitamins and mineras. The information has ed directy to many improvements in nutrition and heath. The chaenge is to extend benefits to the deveoping word. Investigations can be carried out in key areas of heath and nutrition. These incude: MALNUTRITION S TOLL ON CHILDREN DISTRIBUTION OF 10.4 MILLION DEATHS IN DEVELOPING COUNTRIES AMONG CHILDREN LESS THAN 5 YEARS OLD Neonata 32% Source:WHO 5522 CONTRASTING CAUSES CAUSES OF DEATH IN THE DEVELOPING & DEVELOPED WORLD 2544 Other 12% Deveoped Word (incuding economies in transition) Manutrition 49% Meases 6% Infectious & parasitic diseases Diseases of the circuatory system Cancers Diseases of the respiratory system Perinata and neonata causes Materna causes Acute Respiratory Infection 12% Maaria 7% Diarrhoea 19% Deveoping Word (incuding east deveoped countries) Other and unknown 3063 causes % deaths % deaths Note: The figures given in thousands refer to the tota annua deaths from each cause in either the deveoped or deveoping word. Thus, athough the proportion of tota deaths from diseases of the circuatory system is higher within the deveoped word, the 5.5 miion deaths are far outstripped by the 9.8 miion deaths from the same diseases in the deveoping word. Source: The Word Heath Report,1997, WHO, Geneva 17

4 MALNUTRITION ACROSS THE HUMAN LIFESPAN Life Stage Nutritiona Disorders Main Consequences Appicabe Nucear Techniques Embryo/Foetus Intrauterine Growth Retardation, Iodine Deficiency Disorders, Foate Deficiency Low birth weight Brain damage Neura tube defect Sti births RIA (T 3, T 4, TSH, foate) Neonate Low birth weight, Iodine Deficiency Disorders Growth retardation Deveopmenta retardation Brain damage Continuing manutrition RIA (T 3, T 4,TSH, foate) Deuterium abeed water (breast mik intake) Stabe isotopes (micronutrients) C and 15 N abeed substrates (macronutrients) Infant & Young Chid Protein-Energy Manutrition, Iodine Deficiency Disorders, Vitamin A Deficiency, Iron Deficiency Anemia, Deveopmenta retardation Increased risk of infection High risk of death Bindness Anemia Growth retardation RIA (ferritin, foate,t 3, T 4,TSH and other hormones) Deuterium abeed water (breast mik intake) Stabe isotopes (micronutrients, e.g. 57 Fe, 67 Zn) C abeed substrates (macronutrients, Heicobacter pyori) 18 Adoescent Protein-Energy Manutrition, Iodine Deficiency Disorders, Iron Deficiency Anemia, Foate Deficiency, Cacium Deficiency Deayed growth spurt Stunted height Deayed/retarded inteectua deveopment Goitre Increased risk of infection Bindness Anemia Inadequate bone mineraization RIA (ferritin, foate,t 3, T 4, TSH and other hormones) Douby abeed water (energy expenditure) Stabe isotopes (micronutrients) C abeed substrates (macronutrients, Heicobacter pyori) DEXA (bone density, body composition) Pregnant & Lactating Mothers Protein-Energy Manutrition, Iodine Deficiency Disorders, Vitamin A Deficiency, Iron Deficiency Anemia, Foate Deficiency, Cacium Deficiency Materna anemia Materna mortaity Increased risk of infection Night bindness/bindness Low birth weight/ high risk death rate for fetus RIA (ferritin, foate,t 3,T 4,TSH and other hormones) Deuterium abeed water (breast mik intake) Stabe isotopes (micronutrients) C abeed substrates (macronutrients, Heicobacter pyori) DEXA (bone density, body composition) Aduts Protein-Energy Manutrition, Iron Deficiency Anemia, Obesity, Cancer Thinness Lethargy Obesity Heart disease Diabetes Hypertension/stroke Anemia RIA (ferritin, hormones e.g. insuin) Douby abeed water (energy expenditure) Stabe isotopes (micronutrients) C abeed substrates (macronutrients, Heicobacter pyori) DEXA (body composition) Edery Protein-Energy Manutrition, Iron Deficiency Anemia, Obesity, Cancer, Osteoporosis Thinness Obesity Spine and hip fractures & Accidents Heart disease Diabetes RIA (ferritin, hormones) Douby abeed water (energy expenditure) Stabe isotopes (micronutrients) C abeed substrates (macronutrients, Heicobacter pyori) DEXA (bone density, body composition) Deuterium abeed water (body composition) Notes: DEXA = Dua Energy X-Ray Absorptiometry; RIA = Radioimmunoassay TSH = Thyroid Stimuating Hormone T 4 = Thyroxin Source: Modified from WHO/NHD/99.9

5 NUCLEAR & ISOTOPE TECHNIQUES IN HEALTH & NUTRITIONAL STUDIES Assessment of Mi c ro n u t rient Ma n u t ri t i o n. St a b e isotopes provide the ony direct way for the m e a s u rement of iron uptake and bio-ava i a b i i t y. T h e y h a ve come to be re g a rded as a kind of god standard for iron studies in humans and other studies in nutrient bioavaiabiity (e.g. iron, zinc, and vitamin A). Isotope diution methods are used in the assessment of vitamin A status. The principe reies on abeed c a rotenoid conversions to vitamin A, which can be traced with carbon- carotenoids. This way, vitamin A poo s i zes are measured by the diution of an ora ingested tracer into the different body poos. This technique has potentia appications in measuring the effectiveness of vitamin A and carotenoid suppementation and fortification regimes in nutrition studies. Another powe rfu use for stabe isotopes is in the assessment of trace eement bio-avaiabity and poo size s for trace eements, such as iron (iron-57 and iro n ) and zinc (zinc-67 and zinc-70). The uptake of these abeed micronutrients can be traced in vivo. T h i s a p p roach has proved vauabe in measuring the e f f e c t i veness of nutrition suppementation or fort i f i c a t i o n trias in severa deveoping countries. Detection of Infections. Carbon- breath tests are used to examine bacteria coonization in the stomach by Heicobacter pyori. The test measures the production rate of 1 3 C O 2 in expired air, foowed by ora ingestion of 1 3 C-abeed urea. The tests using stabe isotopes are reiabe and non-invasive toos that can be safey appied in chidren where ver high rates of infection and manutrition are observed. Importanty, the cost of the equipment is not very expensive and can be within the reach of many deveoping countries. Estimation of Tota En e r gy Ex p e n d i t u re. The doubyabeed water method ( 2 H O) is the ony technique that can accuratey determine the energy needs of peope in their own environments and is one of the most re i a b e methods for determining food energy intake. This method is gaining wider acceptance since it is inexpensive, accurate, and can be appied under fied conditions. When douby abeed water is administered to a subject, both isotopes mix with body water and are eiminated in body fuids over a period of days. T h e turnover of body water can be estimated from the daiy m e a s u rements of hyd rogen-2 (deuterium) concentration in urine or saiva sampes. When the sampes are anaysed for oxygen-18, the vaues wi refect a more rapid e xc retion rate than that for hyd rogen-2 because the oxygen-18 is aso incorporated into exhaed carbon d i oxide. The difference in exc retion rates between ox y g e n - 18 and hyd rogen-2 tracers thus refects the voume of carbon dioxide produced over the period of observa t i o n. This parameter can be used to cacuate the tota energy expenditure of a subject. Determination of Lean Body Mass. A tracer dose of water abeed with hyd rogen-2 and oxygen-18 is a d m i n i s t e red and aowed to equiibrate for four to six hours. The isotope concentration in saiva or urine wi refect the diution undergone by the isotope. When the ean body mass is cacuated, the difference in body we i g h t is the amount of adipose (fatty) tissue. Me a s u rement of Overa Ni t rogen Fux. The nitro g e n - fux baance stumbes in periods of stress, then the cataboic p rocesses predominate over synthetic processes and a n e g a t i ve baance is the resut. Whoe body protein turnove r is measured by administration of a singe ora dose of an amino acid, or preferaby a protein, abeed with nitro g e n Urine is coected for nine to twe ve hours and the amounts of tracer nitrogen in urinary NH 3 and in the u rea are determined. These two vaues provide a re i a b e estimation of whoe-body protein turnover that is i n s e n s i t i ve to changes in nonpro t e i n - n i t rogen metaboism. Nu t rient Absorption and Ut i i z a t i o n. Weaning infants often have periods of infection eading to diarrhoea. During these periods nutrient intake is insufficient to maintain infant growth and regeneration of sma intestina capacity is essentia. When rice abeed with carbon- (exposed to 1 3 C O 2 during periods of photosynthesis) is cooked and eaten, digestion and absorption of the starch can be detected from the appearance of abeed 1 3 C O 2 in breath sampes. T h e d e g ree of maabsorption can be estimated from the re c ove ry of tracer carbon in tota stoo carbon. Anaysis of Foods. Ne u t ron activation anaysis (NAA) is very effective due to its exceptiona sensitivity and the possibiity of simutaneous determination of severa trace eements. In d u c t i vey Couped Pasma Mass Sp e c t ro m e t ry (ICP-MS) aso offers mutieement determinations. Appication of NAA-reated methods is part i c u a r y a t t r a c t i ve for deveoping countries since many re s e a rc h reactors are avaiabe to provide the needed neutro n source. Air Poution Me a s u rement. Nucear and re a t e d anaytica techniques are uniquey suited for conducting n o n - d e s t ru c t i ve muti-eement anayses of air part i c u a t e matter coected on fiters. Commony used techniques incude: ICP-MS, NAA, Pa rt i c e - Induced X-ray Em i s s i o n, Pa rt i c e - Induced Gamma-ray Emission, Energy Di s p e r s i ve X-ray Fuorescence Anaysis, and Tota Refection X-ray Fuorescence. 19

6 20 n Assessment of Nutritiona Status and Nutrient Requirements; n Assessment of Micronutrient Manutrition; n Detection of Infections; n Anaysis of Foods; n Air Poution Measurement. (See box on page 19 for exampes of appications.) STABLE ISOTOPES IN IAEA-SUPPORTED NUTRITION STUDIES Many factors are important to nutritiona assessments of infants, chidren, pregnant women, and nursing mothers, as we as peope who subsist on margina food suppies. They incude the measurement of breast-mik intake, energy expenditure, micronutrient status, macronutrient utiization, and body composition. Stabe isotopic tracers are safe and noninvasive techniques. They emit no externay measurabe radiation and their presence in excess of natura eves is detectabe ony by changes in the ratio of minor isotope to major isotope. The ratio is measured by an isotope ratio mass spectrometer in which heavy and ight forms of the same moecue undergo separation and quantification. The costs of anaysis are indeed a cause for concern since the instrumentation and expertise required are not avaiabe in many countries. However, stabe isotopes for IAEA-supported studies are made avaiabe under the project, and in some cases assistance is aso provided for anaysis in an IAEA recognized aboratory. The underying idea is that these studies woud encourage the strengthening of infrastructure at nationa faciities for subsequent investigations. The major isotopes (hydrogen-1, carbon-12, nitrogen-14, or oxygen-18) are aways accompanied by a constant proportion of minor heavier isotopes whose individua abundance range from 0.02% to 1.11%. An inventory of the human body shows that a 50-kiogram individua has an aggregate of 225 grams of hydrogen-2, carbon-, nitrogen-15, oxygen-17, and oxygen-18. Athough there are variations in the respective ratios of minor to major isotopes, each major isotope has a characteristic baseine abundance to which tracer measurements are referred. Stabe isotopes can be administered oray and the metaboic products into which they enter (e.g. body water, respiratory carbon dioxide, urea) can be samped in breath, saiva, mik, urine, and stoo. There are severa strategic appications of nucear and isotopic techniques supported by the IAEA. Indeed some of these techniques possess very specia features and specificity, thus rendering them unique in their suitabiity for studies in specific fieds of human nutrition. To date, isotopic strategies evoved through IAEA efforts are practiced in more than 50 Member States. A few exampes are cited beow: Technica Cooperation Projects. A regiona technica cooperation programme invoving Argentina, Brazi, Chie, Cuba, and Mexico appied isotopes for evauating nutrition intervention programmes. The nationa project in Chie competed a study using isotope techniques for various needs. Scientists measured iron bio-avaiabiity in fortified mik of the Nationa Compementary Food Programme, the bioavaiabiity of zinc and body composition in chidren, and the body composition and energy expenditure in preschoo chidren. Esewhere, the first phase of a regiona project in East Asia and Pacific yieded practica resuts. Studies measured the effectiveness of muti-nutrient suppementation using stabe isotopic techniques to assess zinc and iron bio-avaiabiity in seven participant countries, China, Indonesia, Maaysia, Pakistan, Phiippines,Thaiand, and Viet Nam. Additionay, to target manutrition, the IAEA has been deveoping non-invasive isotopic tracer techniques for measuring whoe body vitamin A under conditions of suppementation (Ghana, Peru), food fortification (Peru, Israe) and dietary improvement (China, Thaiand, Phiippines and India). Probems of vitamin A nutrition in chidren and pregnant or actating women are the primary focus. Coordinated Research Projects (CRPs). A CRP on osteoporosis examined differences in bone minera density (BMD)of young aduts across a range of races in a tota of 3752 subjects recruited at 11 centres in nine countries. Highy significant differences in mean weight, height, and BMD between countries was found. Foowing adjustment for age, weight and height,

7 differences in BMD persisted between centres for both men and women. Significant differences existed in young adut bone mass which, if persisting into od age, may contribute to two- to threefod fod difference in fracture risk. A CRP on the physioogica modeing of a Reference Asian Man invoved severa Asian countries and generated reiabe data sets for dietary intake that a can use. Among other appications, this wi enhance their abiity in resoving nationa probems of radioogica protection. It wi aso strengthen capabiities to address nutritiona issues through improved reference vaues that were derived for a number of additiona eements and reference materia matrices. Another project focused on the isotopic evauations of materna and chid nutrition to hep prevent stunted growth. Pakistan and participating countries in Latin America refined and appied isotopic techniques in fied studies. The techniques aso are being used in a CRP to evauate the monitoring of infant growth, in coaboration with the WHO Growth Monitoring Programme. Significant progress through fied work aso has been made against persistent diarrhoea, which accounts for a significant percentage of infant diarrhoea deaths in many countries. The work invoved countries from Africa, Asia and Latin America which joined a CRP on Heicobacter pyori infection and manutrition particuary among the young. Isotopic techniques using carbon- breath tests were successfuy used.investigations covered bacteria coonization and digestion and absorption of nutrients to examine the significance of Heicobacter pyori and its consequence on poor nutrient assimiation in young chidren. FUTURE PROSPECTS A consutant s meeting caed by the IAEA in December 2000 offered insights into the future appications of stabe isotopes in nutrition research. Nove appications were identified by improving existing techniques to extend the usefuness of stabe isotope techniques in minera and trace eement nutrition research and to aow their use more routiney. Exampes incude: n Recent investigations have shown that cacium in the skeeton can be abeed using the isotope cacium-41. This offers the unique opportunity to ook at cacium osses and baance in bone directy via urinary excretion of the isotopic abe. n Based on the simutaneous excretion of an ora and an intravenousy given abe, the urinary monitoring technique has been vaidated for determination of true cacium absorption; attempts are being made to vaidate this technique for urinary monitoring for zinc and magnesium. n Stabe isotope techniques are used routiney to assess the absorption of iron, copper, zinc, seenium, cacium, and magnesium from test meas. It is possibe to extend the range of appication to other eements, such as moybdenum, nicke, vanadium, tin, and boron, to better understand their bioogica functions. Semistabe, very ong-ived radionucides (auminium-26, manganese-53 and iodine- 129) can be used for monoisotopic eements. n Use of stabe isotope techniques for absorption studies is not imited to those that are essentia to the human body. They can aso be used for toxicoogica studies of ead, mercury, and chromium. For heavy metas, stabe isotope techniques have been used in humans to study cadmium absorption. n Impressive progress is seen in the instrumentation of Isotope Ratio Mass Spectrometry (IRMS) incorporating a gaschromatographic interface. This improvement faciitates specific compounds to be converted to carbon dioxide, hydrogen or nitrogen yieding isotope ratio measurements that are specific to compounds. This is expected to open new and exciting appications in nutritiona sciences. Advances in the fied wi extend the many beneficia appications of isotope techniques for improving human nutrition and heath. These techniques have ony begun to be appied in deveoping countries where they can not ony benefit miions, through improved nutrition, but serve as specific indicators of broader socia and economic advances. In many cases, stabe isotopes provide the ony direct way for gaining information that can directy affect the ives and we-being of men, women, and chidren everywhere. p 21