EUGENE GARFIELDINSTITUTE FOR SCIENTIFIC INFORMATION3501 MARKET ST., PHILADELPHIA, PA 19104

Mapping the World of Nutrition:Citation Analysis Helps D~gest the

Menu of Current Research

Number 47 November 23, 1987

The basic task of nutritional science is $‘toformulate a diet over the lifetime of an in-dividual that will optimize health, well-be-ing, and longevity. Thks calls for providingthe necessary chemical components in theright proportion and avoiding or minimiz-ing toxic substances, ” according to HaroldJ. Morowitz, professor of molecular bio-physics and biochemistry, Yale University,New Haven, Connecticut. I

From this broad definition, it is clear thatthe science of nutrition draws on a varietyof research areas, including biochemisby,physiology, and psychology. Jn past essays,we have discussed topics related to nutrition,such as fcod additives,z fasting, s andanorexia.b

To organize and trace the literature of thediverse research areas pertaining to nutri-tion, as well as to pinpoint’ ‘hot” nutritionalresearch, we use the research-front fdes wehave created from the Science Citation In-dexa (SCP ] and the Social Sciences Cita-tion Indexm (SSCP ).

Research FrontsResearch fronts, or subspeciaky groups

sometimes called invisible colleges, developas authors cite relevant papers “mtheir fields.Using co-citation analysis, we identi~ thosepapers most frequently cited together, orco-cited. Core papers associated in this waymay share key theories, results, methods,or discussion. Table 1 is a selected list ofresearch fronts related to nutrition, cover-ing such areas as diet and cancer, minerals,vitamins, and proteins. Research-frontnames are derived algorithmically using keywords or phrases in the citing literature.

Keep in mind that some fronts may repre-sent complex combinations of topics, sothese labels are by necessity extremely ab-breviated,

Just as we are able to cluster smallergroups of core papers, we can also createhierarchies of research fronts by determin-ing whether citation links exist betweenthese critical “smaller” clusters—clustersthat are, by definition, more specializedareas. We do this in five hierarchical levels.The highest level, the C5 “global” map ofscience, shows the interconnections betweenvery broad areas of knowledge. At the nextlower level of clustering, the identified par-titions are more recognizable as traditional“disciplines” or specialties.

Figure 1 illustrates a C4 map for 1986,showing the major research areas in the so-cial and natural sciences. Nutrition researehtopics are found in the areas designated as“Heart disease” (#86-0131), “Metabo-lism” (#86-0144), and “Physiology”(#86-0096), to name a few. The proximityof points comected by lines on this map isa result of co-citation patterns existing be-tween specialties and can be interpreted asa measure of the degree of field relatedness.Distances between comected points are in-versely proportional to their co-citationstrengths.

Any one of the points on the C4 map canbe explored further by examining ita lowermember clusters on a more specific level.By zooming in on’ ‘Genetics and immrmol-Dgy” in Figure 1, youcancreatethe C3 snapfound in Figure 2. Here, “Molecular biol-Dgy” (#864W73) is “centraf,” although theliterature on immunology is larger. Radi-

349

sting from the central point are various clus-ters concerning both basic and applied nu-trition research, including “Proteins andamino acids” (#86-0353), “Protein syn-thesis” (#86-0888), and “Amino acid se-quences” (#86-1091).

Peripheral areas ofien concern subjectmatter that is less theoretical. For in-stance, “Nutrition in health and disease”(#86-0104), “Carbohydrate biochemist”(#86-0802), and “Dietary fats and cancer”(#86-0455) are located on the periphery ofFigure 2. This means that the literature inthese clusters is less co-cited with the litera-ture in other identified areas. This couldchange in the future. Quite often these areasare in a transitional state until they move incloser or even disappear from subsequentannuaf maps.

Major Nutrienta

Some of the topics in Figure 3 deal withlipids. These compounds, along with car-bohydrates and proteins, fall into the classcalled energy nutrients because the energythey contain may be used by the body forsuch functions as heating, building andrepairing cell structures, and motility. In ad-dition, the energy may be stored in body fatand other compounds for later uses (p. 25)

Lipids, generally called fats, are natural-ly occurring substances that cannot be dis-solved in water. Members of the lipid familyinclude the triglycerides, phospholipids, andsterols, In addition to being a major energyreserve, lipids provide nourishment andstructural support for many tissues.6(p, 105)

In an earlier essay we discussed the im-portant role of cholesterol in the body whenwe described the achievements of Nobel lau-reates Michael S. Brown and Joseph L.Goldstein, University of Texas Health Sci-ence Center, Daflas.7 (Other Nobel Prizesawarded for work concerning cholesterol in-clude the 1928 chemistry prize, to AdolfOtto Reinhold Windaus; the 1964 prize inphysiology or medicine, to Konrad Blochand FeOdor Lynen; and the 1975 chemistryprize, to Sir John Warcup Cornforth andVladimir Prelog, ) Recently, a new drug,

called lovastatin, made headlines in the pop-ular press as an effective remedy to reducehigh cholesterol levels in the blood, whichcan subsequently reduce the risk of heart dis-eases Note that in Figure 3, two prominentfronts deal with cholesterol research—‘‘Low-density lipoprotein cholesterol”(#86-2071) and “Coronary heart disease andlipid research” (#86-3615).

Usually most of the body’s energy is de-rived from carbohydrates, those compoundscomposed of carbon, hydrogen, and oxygen.Carbohydrates are broken down in the bodyinto glucose or other sugars before furthermetabolism. Glucose is absorbed into thebloodstream and travels to specific organs,such as the brain, where it is broken downto provide energy. To store energy for futureuse, glucose may also be converted toglycogen or fat.b (p. 141) However, theamount of glycogen is smaffcompared to thebody’s main stores of energy: fat, in theform of triglycerides.g

In the body, dietary protein is fwst brokendown to amino acids, which contain carbon,hydrogen, oxygen, and nitrogen. Theseamino acids are then resynthesized into thenecessary proteins, which have a variety offunctions in the body. Some proteins are en-zymes that facilitate certain chemical reac-tions. Other proteins are used by the bodyto replace parts of worn-out celfs, buifd newtissues, act as antibodies, and maintainthe water, salt, and acid balances ofthe body’s fluids. The organic part of ex-cess amino acids is changed to glucose orfat; the nitrogen is excreted as ureas(p. 138)

Essential Nutrients

Although the body can make new nutri-mts from carbohydrates, lipids, and pro-teins, there are certain compounds that can-not be synthesized by the body in amountsnecessary for maintaining health. In fact,several of the amino acids are essentiaf, asme two of the fatty acids. These essentialnutrients must be supplied by food.

During the first part of this century, iden-tification and characterization of essential

350

Fiarrre1:MapofC4cluster#86-0001,showing major rexarch areas in the social and mtumlsciences.Linesconnectingnodesrepresentco-chadonstrengths.Thecirclearoundeachnode-.is proportional in area to the number of citing papers. Nanrcs refer to 1986 C3-level SCP /SSCF research fronts. Each of these., in turn. has ifs own group of research fronts.

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nutrients dominated nutritional research.Now the focus is on understanding interre-lationships among nutrients and nutrient in-teractions with physiological systems anddisease processes. Scientists have estab-lished that the macrominerrds (such ascalcium, magnesium, phosphate, potassium,and sodium) and trace minerals (includingiron, zinc, and copper) are required by thebody in specific concentrations for goodhealth.

Mineral research otien focuses on thedietary intake of specific population groups,the availability of minerals from food, andon metabolism. For example, the dietary re-quirements for zinc intake for pregnantwomen are different than those for elderlywomen. In the front on “Iron and zinc nu-tritional status” (#86- 1446), listed in Ta-ble 1, a paper by G.F. Kirsten and col-leagues, Department of Pediatrics and ChildHealth, University of Cape Town and In-stitute of Child Health, Red Cross WarMemorial Children’s Hospital, SouthAfrica, discusses the serum zinc and cop-per levels found in healthy pregnant womenfrom middle and upper socioeconomicclasses. IIJMaternal serum zinc and copperlevels during pregnancy and the months im-mediately following birth show a specifictrend with low zinc and high copper levelsat term. These patterns appear to be causedby normal hormonal changes typical in preg-nancy. 11Normal nonpregnant adult levelsare usually attained 8 to 12 weeks afterdelivery. 10

Vitamin intake and metabolism are alsoimportant research areas. If specific vitaminconcentrations in the body are above or be-low the optimum level, adverse effects mayoccur that can lead to death. The front fromTable 1 on “Vitamin-A toxicity and chron-ic hypervitaminosis-A” (#86-5 186) has 54published papers citing 4 core documents.In one of the core papers in this front, FrankR. Smith and DeWitt S. Goodman, Depart-ment of Medicine, Columbia UniversityCollege of Physicians and Surgeons, NewYork, note the well-known fact that ex-cessive vitamin-A intake can result inskeletal pain, dermatitis, and hepatic inflam-

mation. They studied the mechanism ofvitamin-A transpofi in the body and the ef-fects of excessive dosage. 12

The Recommended Dietary Allowances(RDA) have been established by the Foodand Nutrition Board (FNB) of the NationalAcademy of Sciences/National ResearchCouncil (NAS/NRC). Dietary standardshave also been developed for use in manyother countries as goals for good nutrition.In the UK, for instance, such standards areknown as Recommended Daily Allowances.In a recent article in Chemistry & hrdu.rtry,nutritionist Ann F. Wrdker, University ofReading, UK, notes that “techniques formeasuring human nutritional requirementshave improved and nutritional scientists havenow more confidence in defining minimumphysiological intakes of nutrients than ever~ fore J~I3 Accordingly, reassessments ‘f

recommended nutrient intakes are current-ly occurring throughout the world. Table 2is a selected list of organizations providinginformation on nutrition research.

Recently, the report of the committee pre-paring the 10th edition of the RDA in theUS was rejected by the NAS/NRC. The dis-agreement concerns the fundamental basisfor establishing dietary allowances, accord-ing to Kay B. Franz, Department of FoodSciences and Nutrition, Brigham YoungUniversity, Provo, Utah. 1] Originally, rec-ommended allowances of nutrients were es-tablished at minimum levels necessary toprevent starvation. I’1 Now recommenda-tions are intended to maintain health and arecalculated based on available dietary sourcesand the neds of various population groups,to name just two of the many factors in theequation. 11A new factor—the possible in-teraction between nutrient intake and dis-ease—may have been introduced by theFNB’s rejection of the RDA committee’srecommendations. The committee had sug-gested that the RDAs for vitamins A and Dbe lowered, but the FNB objected, believ-ing that these nutrients may be beneficial in:ancer prevention. I3Deficiency Diaeaaes

The importanceof certain nutrients in theiiet became obvious centuries ago from the

352

353

Figure 3: MapofC2cluster#864104,4‘Nutritionin health and disease, ” showing some major areas of researchfor 1986. Numbers of core/cifing papers for each C 1 front are show” atier the research-front name.

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nundxr of dkease8 that &velo@ as a resultof poor diet. For example, with the advancesin navigation and cartography in the late fif-teenth century, prolonged sea voyages be-came possible. Sailors were forced to sub-sist for extended periods on biscuits, saltedmeat, cheese, and dried legumes. Scurvy be-came a feared disease for seafarers. JacquesCartier, a French navigator and explorer,described the symptoms of the dk,ease af-fecting his crew: “Some did lose all theirstrength and could not stand on their feet.Their legs became swollen, the sinews con-tracted and turned black as coal . . . . Othershad their skin spotted with spots of bloodof a purple color .. . . Their mouths becamestinking, their gums so rotten that all theflesh did fall off, even to the root of theteeth.”ls

In 1747 British physician James Lind con-ducted the first experiment to find the besttreatment for scurvy. He found that citrusfluits promoted a speedy recovery from thedisease. However, it wasn’t until the 1920sthat it was firmly established that scurvy wascaused by a vitamin-C deficiency. 15Today,research on vitamin C (ascorbic acid) in-cludes studies to determine the most bene-ficial levels of this vitamin in the body. Ta-ble 1 includes a front on “Ascorbic acidlevels” (#86-4955), which contains 32 citingpapers.

In 1937 Sir Walter N. Haworth, Birming-ham University, UK, was awarded the No-bel Prize in chemistry for hk investigationson carbohydrates and vitamin C. And ofcourse, Nobelist Linus C. Patthng has longbeen a proponent of the curative potentialof vitamin C, including the presumed pre-vention of cancer.

Hippocrates prescribed ox liver, a richsource of vitamin A, for the cure of nightblindness, a sign of vitamin-A deficiency. 1ITite importance of vitamin A was indirect-ly rediscovered in 1909 by German physi-cian Wilhelm Stepp, who found that egg-yolk extracts contained a fat-soluble materialthat is necessary for good health. 115VitaminA was called a “fat-soluble accessory” in1915 by Elmer V. McCoHum andMarguerite Davis, University of Wisconsin,Madison, to differentiate it from other healthfactors that were water soluble. 11,17In ad-dition to liver and egg yolk, foods that in-clude vitamin A include butterfat, fish-liveroil, and yellow-orange fruits and vegetableslike carrots, sweet potatoes, cantaloupes,and peaches. ~g

Vitamin A plays two roles in keeping theeye healthy. In the retina, vitamin A is re-quired for normal functioning of the visualpigment; a deficiency results in night blind-ness. Vitamin A is also needed by the cor-nea; a deficiency causes the cornea to grad-

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Table 1: Selcctcd list of 1986 SC~ /SSCF macmch fronts dcahrrg with varinus aspects of human nutrition.A = number of core papers. B= number of citing papers

86-112886-36718&7528

86-352686-528186-8504

86-024086-1065

86-054886-144686-326386-342986-536686-547386-7003

86-163086-186286-275786-291186-361986409686-521886-550186-6772

86-111986-4562

86-197986-252786-367186-390786-423886-464386-495586-518686-534486-557786-594886-636486-787986-8147

Name

CANCER.4NDNuTftfT1ONNutrition and diet in the etiology of cancerNutritionrd antioxidarrts and cancer prevention through nutritionVitamin A in cancer; cellular retinol binding protein

FIBERDietary fiber and fecal bulkingDietary tihcr and wheat bran supplementsNutrition in cancer and dtetary tibcr in breast cancer etiology

MALNUTRITION

Nutrition in KenyaMalnutrition in hospitalized patients and metabolic management of critically ill surgical

patients

MINERALS

Low dietary zinc intakeIron and zinc nutritional statusIndexes of mineral metabolismZinc supplerrmntation in anorexia nervosa and functional consequences of zinc deficiencyClinical zinc deficiency and zinc metabolism during total parenteral nutritionCopper and zinc deficienciesTrace elements in nutrition; excesses and deficiencies of copper and zinc

PROTEINS AND AMINO ACIDS

Leucine metabolism and plasma amino acidsBenefits of a low protein, essential amino acid, keto acid dietOral aspartame, plasma amino acid ratios, and various protein concentrationsNutritional quality of avaifable Iysine and other free amino acidsPlasma amino acid metabolismEffect of leucirre and amino acid transponMethionine metabolism and S-adenosyl amino acidsPlasma arginine, brain tryptophan, and branched-chain amino acidsProtein markers and nutritional asacssment

SALTS

Dietary calcium intake and calcium’s role in hypertensionSodium chloridedepcrrdent hypertension and high salt diets

VfTAMINS

Biosynthesis of vitamin B 12Serum retinol and vitamin E in an alcoholic populationVitarrrirr-C radicafs and numitional antinxidsntsMetahnlism of vitamin B6Vitamin-D supplementation in pregnancyViramin-B12 deficiencyandfolateindepressionAscorbicacidIeveIaVitamin-Atoxicityandchronichypervbaminosis-AVbanrin-B6deficiencyandba effect on lung elastin crosslinkingVitamin-A stability and nutrient supplementsRiboflavin status and pediatric multiple-vitamin preparationsVitamin-K deficiencyAscorbic acid copper-ion systemSerum vitamin-Dmetabolizes and bone meeabdism

AB

7 1284 383 152

12 1232 162 45

8 5120 201

66019 1552 382 164406 462 19

6 596 69

30 3625 414 98

10 1123 348 773 31

59 6296 50

7 414 544 38

13 762 162 152 324 542 333 252 145 323 282 35

355

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79-0660Vitam(n. D regula

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ttally deteriorate, a major cause of blindnessin children in many countries. 1I In 1967George Wald, Harvard University, receivedthe Nobel Prize for elucidating the role ofvitamin A in vision. Goodman cites esti-mates that about 500,000 new cases of vi-tamin-A deficiency with active comeal in-volvement occur amually in India, Bangla-desh, Indonesia, and the Phdippines. Thisfigure does not include other areas wherethe disease is known to occur, such asAfrica, Central and South America, or theMiddle East. 19

Neville R. Bekon, Department of ChildLife and Health, University of Edinburgh,Scotland, notes that another worldwideproblem is a bone disorder that is calledrickets when it affects infants and children;it is known as osteomalacia when it occursin adults. zo The condition is caused by adeficiency of vitamin D, which regulates theintestinal absorption of calcium and phos-

L-__-_Jcam momsceils andretinoids1 1,/260

phorus by the bones and teeth in the body.In rickets, a lack of vitamin D causescalcium to be poorly absorbed from the diet,which in turn prevents normal bone forma-tion; bones weaken and become deformed.In osteomalacia, although the protein matrixsupporting the bone is properly formed, itis not properly calcified, making the bonessoft and pliable. The result is bone pain andmicrofractures. i 1.21

Vitamin D is unique in that it can be ob-tained by the body without the help of food.The vitamin is formed when ultraviolet raysof the sun strike 7dehydrcxholesterol, a fat-ty substance just under the skin. zo Bekon’spaper is included in the research front on‘‘Vitamirt-Dsupplementation in pregnancy”(#86-4238), found in Table 1.

The precise role of vitamins A and D inthe body is still being investigated. To docu-ment the progress of this research, we havedeveloped a historiograph on the effects of

356

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84.628255/461 vitamin D and

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mvitamins A and D in health and disease (seeFigure 4). Each box includes the name ofthe research front, as well as the number ofcore articles and citing (published) papers.The fronts that are included are determinedby the continuity of the core literature fromyear to year. If the same core documents arecited at the required thresholds in two adja-cent years, then a “string” is established.By continuing thk procedure, a historio-graph is developed.

Not all deficiency diseases arise from alack of vitamins; they may instead resultfrom mineral deficiencies. For instance, al-though iron is one of the most abundant mine-rals on earth, iron deficiency may be themost prevalent nutritional problem in theUnited States. Iron is an important part ofthe hemoglobin molecule, which is neces-sary to transport oxygen from the lungs tothe tissues. While iron deficiency causesphysical problems, Betsy Lozoff and Gary

A A in cancer i

1._3E_JM. Brittenham, Case Western Reserve Uni-versity, Cleveland, Ohio, cite evidence thata lack of iron may adversely affect behav-ior by causing diminished attention span, in-telligence, and learning ability; apathy; ir-ritability; and tension. These problems canhave enduring consequences for infants andchildren by interfering with pro~r develop-ment.zz Lozoff and Brittenham’s paper ispart of the current literature that cites intofront #86-1446, “Iron and zinc nutritionalstatus” (mentioned earlier).

?Xet and Cancer

A favorite theme in the popular press isthe newly discovered cancer-fighting or can-cer-promoting foods, ranging from bacon,bran, and broccoli to calcium, carrots, andcoffee. These claims may lead the reader tobelieve that cancer prevention is only a mat-ter of eating the correct foods, whereas theproblem is actually more complicated. Other

357

Table 2: Selected list of organizations supporting research and dissemimting information on nutrition

American Bnard of Nutrition6212-B Old Kcene MillCourtSpringfield,VA 22152

American College of NutritionP.O. ~X 831White Plains, NY llX432

American Dietetic Association430 North Michigan AvenueChicago, IL 6C411

American Institute of Nutrition%50 RnckviUe PikeBethesda, MD 20814

American %ciety for Parenteral and EnteralNutrition

8605 Cameron Street, Suite 5C0Silver Spring, MD 20910

Commonwealth Bureau of NutritionRowett Restach InstituteBucksburn, Aberdeen AB2 9SBUnited Kingdom

Fnnd and Nutrition BoardNational Research Council2101 Cons!ihrtion Avenue, NWWashington, DC 20418

factors in addition to diet play a role in can-cer, such as familial risk of cancer, exer-cise regimen, and contact with environmen-tal hazards.

Although there is no simple explanationabout the role that diet may play in cancerprevention, many scientists have found atentative link between certain types of foodand some forms of cancer. For instance,Bruce Armstrong and Richard Doll,Radcliffe Infirmary, Oxford, UK, note thatthere is a strong correlation in developedcountries between fat consumption andcancer deaths.zs David J.A. Jenkins andcolleagues, Department of NutritionalSciences, University of Toronto, Canada,state that a number of hypothesm have beendeveloped to explain the mechanism for thepromotional effect of fat in cancer. One cur-rent theory suggests that increasd intake offat may result in the increased loss of bileacids to the colon, which may damage thecolonic mucosal cells and result in cancerof the colon. 24

Other evidence suggests, however, that itis not fat intake that contributes to cancerand heart disease but, instead, excessivecaloric intake and obesity. 1I A study by

Institute of Nutrition of Central America andPanama

Carretera Roos@velt-Zom 11Aptdo postal 11-88Guatemala, Guatemala

International Life Sciences Jnstitute-NutritionFoundation

1126 16th Street, NWWashington, DC 20036

Intermit ional Union of Nutritional SciencesInstitute of Biology41 Queen’s GateLondon SW7 5HUUnited K@dom

Joint FAO/WHO/OAU Regioml Fond andNutrition Commission for Africa

FAO Regional Office for AfricaP.O. BOX 1628Accra, Ghana

Society for Nutrition Education1700 Broadway, Suite 300Oakland. CA 94612

Jaakko Tuomilehto, Department of Epide-miology, National Public Health Institute,Helsinki, and colleagues at the institute andthe Department of Community Health, Uni-versity of Kuopio, Finland, found that menwith a high body mass were significantlymore likely to have heart attacks than theirnormal peers. 25 Other studies have foundthat diets that were high in total calories-re-gardless of their Percentage of fat, protein,and carbohydrates-were associated with ahigher risk of various forms of cancer inboth ratszb and humans.z7

While increased fat or calorie intake maypromote cancer, fiber intake may preventsome types of cancer. However, the exactmwhanism of fiber in cancer prevention ha8not yet been defined. Dietary fiber is actual-ly a general term for various complex plantsubstances that are partially or completelyindigestible. These include water-soluble fi-bers found in plant stems, seeds, and fruit,and water-insoluble fibers found in cerealgrains and vegetable skims (p. 76) Table 1contains three fronts concerning fiberresearch.

A landmark in stimulating interest in thisresearch area was a 1971 article by Denis

358

P. Burkitt, Unit of Orographical Pathology,St. Thomas Hospital, London, UK, who ob-served that some African tribes eating a diethigh in unprocessed, fiber-rich foods hadlower rates of certain cancers than did West-ern populations .28 According to DavidKritchevsky, Wistar Institute, Philadel-phia, g Burkitt’s interest in this area wasstimulated by a 1956 paper by T. L. Cleave,surgeon captain, Royal Navy, UK, in whichCleave suggested that many modem ills aredue to the ingestion of refined sugar andflour.zg Cleave’s paper has been cited 43times—9 of them by Burkitt-according tothe SCI.

One theory regarding the mechanism offiber in cancer prevention was proposed byBurkitt in a 1981 Citation Classicm. Hewrote that “any carcinogens concentratedin a small faecal volume and retained a longperiod in the gut might be more dangerousthan those diluted in a large faecal volume,moved along more quickly, and excretedmore often” as a result of fiber intake. so

The research front on “Nutrition in can-cer and dietary fiber in breast cancer etiol-ogy” (#86-8504), found in Table 1, containsa review paper by Kritchevsky on the roleof fiber. He notes that there are problemsin ftiing strong evidence that fiber can helpprevent cancer. One problem stems from thedifferences in methodology and sources ofdietary data. In addhion, the average per-son generally eats fiber-rich foods, not spe-cific fibers alone, The other components in-cluded in fiber-rich foods may act as addi-tional variables in the methodology. ~1

Vitamin A is a recent arrival to the cancerprevention scene. K.A. Madani and Mo-hamed B. Elmongy, Department of Nutri-tion, Tulane University School of PublicHealth and Tropical Medicine, New Or-leans, Louisiana, note that in a cancerousdisease malignancies occur when the pro-cess of cellular differentiation is lost. Reti-noids, which are analogues of vitamin A,are known to be involved in the enhance-ment of cell differentiation. Madani and El-mongy review several possibilities for themechanism of action of retinoids in cancerprevention.3Z This paper is included in the

front on “Vitamin A in cancer; celhdar re-tinol binding protein” (#86-7528), found inTable 1.

Other papers suggest that the dietary in-take of a precursor of vitamin A, calledbeta-carotene, is more closely linked witha lowered risk of developing cancer than isthe ingestion of vitamin A itself.33,34 Car-~tenoids are found in carrots, green leafyvegetables, and some yellow and red fruitsand vegetables; retinoids and vitamin A oc-cur chiefly in foods of animal origin, suchas milk, cheese, butter, egg yolk, andliver.~

ConclusionWe have touched upon just some of the

issues that dominate nutrition research to-day. A future essay will discuss nutritionjournals. Judging by the C4 map in Figure1, nutrition research is so diverse that it isimpossible to assign it any single major pointof reference. It will be interesting to studythe impact of journals devoted solely to nu-trition and to observe how they interact withjournals in other disciplines, such as bio-chemistry.

However, the multidisciplinary characterof thk field increases the difficulties in alter-ing the attitudes of researchers and clini-cians. UntiJ now, nutritional science has notbeen given the priority it needs in medicaltraining. As this essay went to press, Ilearned about a new program at TheRockefeller University, New York, spon-sored by the Pew Memorial Trust. Medicalstudents completing their first year of studywill spend one year in the Rockefellerlaboratories, learning the methods of basic,fundamental science as applied to problemsin human nutrition. Jules Hirsch, professorand senior physician, who is in charge ofthe program, has told me that it is the aimof these fellowships to interest medicalstudents in careers as physician-scientists in-vestigating the important issues of humannutrition. 35

*****

My thanks to Stephen A. Bonaduce, C.J.Fiscus, and Lisa Holland and for their helpin the preparation of this essay.

19871s1

359

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1. Morowitz H J. Food for thought. The w“ne of lifeandorkeressayson sociti”es, errergy & living things.New York: St. Martin’sPress,1979,p. 236-40.

2, Garfield E. Toward ending the ecurfusion surrounding foarf additives: the rase for beercr labeling.Ersays of an informationscientfir.Phila&lphia:1S1Press,19LI1. Vol.4, p. 180-92.

3. -——, To fastor nottonmuchfast.Parta1& 2. ibid., 1983. Vol. 5, p. 313-26.4. -—, Anorexia nervow the enigma of self-starvation. fbid., 1985. Vol. 7. p. 240-50.5. Hmrdftorr E M N & Wfdtrmy E N. Nutrition: concepts and controversies.

St. Paul, MN: West, 1979.629 p.6. Yetiv J Z. Popub nutritional practices: a scient@c oppraisal.

Toledo, OH: Pqrufar Medicine Press, 1986.318 p.

7. Garfield E. The 1985 Nobel Prize in medicine-Michael S. Brown and Joseph L. Goldstein haverevolutionized our knowledge ahnut cholesterol metabolism and heart disease.Current Contents (38):3-13, 22 September 1986.

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