- Email: [email protected]
Vitamin A supplementation and HIV-1 mother-to-child transmission in Africa
CORRESPONDENCE
small-for-gestational-age babies. Second, the comparability of the two groups during pregnancy is not described, and possible differences might have occurred despite randomisation, especially in a factorial design. Third, the reported compliance of 91% is very high for a trial with 4 months of treatment in an African population, but no objective information was presented about a possible difference of compliance between the group of women who received multivitamins and the group who did not. Women receiving multivitamins may have rapidly felt in better shape (especially for vitamin C supplementation), and their compliance could have been better than in the group who did not receive this intervention, in which there were women receiving vitamin A alone. Moreover, we have no details of the maternal characteristics at the beginning and end of pregnancy: some that could affect pregnancy outcome, such as maternal body weight gain or other clinical indices, and be improved by multivitamin supplementation, could have reduced the power to detect a difference in the vitamin A comparison. We also have reservations about the feasibility of such an intervention early in pregnancy since most African women use prenatal services late in pregnancy.2 In this Tanzanian trial setting, the selection process of eligible women and the characteristics of women enrolled could have partly accounted for some of the positive results—eg, high HIV-1 screening and trial acceptability, or high drug compliance. Finally, Fawzi and co-workers offer reasons for the absence of beneficial effects of vitamin A supplementation. However, the essential objective of their trial has not yet been achieved— namely, a benefit of vitamin A supplementation on maternal and infant morbidity, as has already been suggested in other such trials.3,4 We, as are many researchers in prevention of vertical transmission of HIV-1 in developing countries,5 are pleased to hear about the potential benefit effect of multivitamin supplementation but are waiting for information on the association between vitamin A supplementation and evolution of women’s health, HIV-1 mother-tochild transmission, and child morbidity. *Katia Castetbon, Valériane Leroy, François Dabis INSERM U330, Université Victor SegalenBordeaux 2, 33 076 Bordeaux, France
654
1
2
3
4
5
Fawzi WW, Msamanga GI, Speigelman D, et al. Randomised trial of effects of vitamin supplements on pregnancy outcomes and T cell counts in HIV-1-infected women in Tanzania. Lancet 1998; 351: 1477–82. Mtimavalye L, Biggar RJ, Taha TE, Chiphangwi J. Maternal-infant transmission of HIV-1. N Engl J Med 1995; 332: 890–91. Coutsoudis A, Bobat RA, Coovadia HM, Kuhn L, Tsai WY, Stein ZA. The effects of vitamin A supplementation on the morbidity of children born to HIV-infected women. Am J Publ Hlth 1995; 85: 1076–81. Coutsoudis A, Moodley D, Pillay K, et al. Effects of vitamin A supplementation on viral load in HIV-1-infected pregnant women. J Acquir Immune Defic Syndr Hum Retrovirol 1997; 15: 86–87. Dabis F, Msellati P, Newell ML, et al. Methodology of intervention trials to reduce mother to child transmission of HIV with special reference to developing countries. AIDS 1995; 9 (suppl A): S67–74.
Sir—Wafaie Fawzi and colleagues’ results1 bring potent arguments for the use of vitamin supplements to reduce adverse pregnancy outcome in African HIV-1 infected women. Data and interpretation of the effect of vitamins on T-cell counts, however, raise questions that should be addressed before such an intervention is applied. Can the mechanism by which vitamins increase CD4 cell counts slow the process of HIV disease progression? It is well known that HIV-induced alterations are distinct according to the T cell subsets, mainly including a concomitant rise in CD8 activated T cells and a fall in CD4 cells, this last event being a multifactorial process. Peripheral cell loss results from decreased proliferation, increased cell death by apoptosis, increased emigration to lymph nodes, and, but this last mechanism is controversial, reduced central T cell production.2 The global rise noted by Fawzi and co-workers in all peripheral mature T subsets, rather than in CD4 cells alone, suggests an impact on the last process—ie, proliferation of leucocyte progenitors.3 Data on total white blood cells, differential white cell counts, total lymphocyte counts (which are often proposed as an alternative to CD4 counts in the African setting4), and CD4/CD8 ratio should be discussed. A trophic effect on both fetal cells and haematological precursors, rather than a real immunological T cell improvement, could well result from the use of folic acid and vitamin B12, micronutrients which have key roles in the metabolism of proliferating cells. Is the increase seen in CD4 cells, resulting from this whole T lymphocyte population enlargement, protective against opportunistic diseases? The value of absolute CD4 cell count as a surrogate marker of
progression to AIDS has been confirmed in a prospective study. 5 Nevertheless, this fact does not anticipate the functional value of expanded CD4 cells during treatment. In fact, the relation between the gain in CD4 and the protection against pathogens in treated patients is being intensively researched. Could generalisation of multivitamin supplementation in HIVinfected people have adverse effects? Although an increase in viral load is not likely to occur, this load should be monitored. Alternatively, a theoretical risk of some protozoal opportunistic diseases such as toxoplasmosis should result from the widespread use of folate supplementation. Indeed, this risk could undermine folic acid antagonists administration, one of the rare weapons for the prevention of AIDS in developing countries.4 Eric Ledru Viral Oncology Unit, Pasteur Institute, 75724 Paris, France (e-mail: [email protected]) 1
2
3
4
5
Fawzi WW, Msamanga GI, Spiegelman D, et al. Randomised trial of effects of vitamin supplements on pregnancy outcomes and T cell counts in HIV-1-infected women in Tanzania. Lancet 1998; 351: 1477–82. Rosenberg YJ, Anderson AO, Pabst R. HIV-induced decline in blood CD4/CD8 ratios: viral killing or altered lymphocyte trafficking? Immunol Today 1998; 19: 10–17. Beutler E, Lichtman MA, Coller BS, Kippl TJ. Williams hematology, fifth ed. New York: McGraw-Hill, 1995. Ledru E, Diagbouga S, Meda N, et al. A proposal for basic management of HIV disease in West-Africa. Use of clinical staging and haemogram data. Int J STD AIDS (in press). Perneger TV, Yerly S, Perrin L. Transforming laboratory test results to improve clinical outcome predictors in HIV patients. J Acq Immun Defic Syndr Hum Retroviral 1998; 17: 442–49.
Authors’ reply Sir—We agree with Katia Castetbon and colleagues that we have limited power to detect small effects of vitamin A on adverse pregnancy outcomes. We also stated that the confidence intervals of our results are compatible with a modest protective assocation of vitamin A, although it was smaller than the effect of multivitamins and was not statistically significant. In addition, we reported that there were no significant differences between treatment arms in various baseline characteristics. There were also no differences in compliance between treatment arms, as measured by pill counts of supplements or ingestion of the vitamin A dose at delivery. Women who received vitamin A supplements had significant
THE LANCET • Vol 352 • August 22, 1998
CORRESPONDENCE
improvements in serum vitamin A concentrations compared with those who did not. The effect of vitamin A was unlikely to be obscured by possible effects of multivitamins on maternal weight or clinical stage of disease. The effects of vitamin A or multivitamins were not modified by baseline body mass index or CD 4 cell counts. Furthermore, there was no interaction between the effect of vitamin A and that of multivitamins without vitamin A on adverse pregnancy outcomes or on maternal T cell counts. Our findings are generalisable to women who present to prenatal care during the second trimester. In our Tanzanian study, the median gestation age at enrolment was 5·3 months. This time is similar to the median gestation age at presentation to antenatal services among women in the general population who participated in the demographic and health surveys of Tanzania (5·6 months), 1 Uganda (5·9),2 Zambia (5·6),3 and Zimbabwe (5·1).4 Thus, we believe that provision of vitamin supplements from the fifth month of pregnancy is potentially feasible. We agree with Eric Ledru that it is important to assess both the efficacy and any potential adverse effects of the multivitamin supplements on progression of HIV disease and the risk of opportunistic infections. We are examining the effect of both treatments on these endpoints and on vertical transmission and infant mortality. Similar to the effects of CD4 and CD8 cell counts, multivitamins but not vitamin A resulted in an improvement in CD4/CD8 ratio. Neither vitamin A nor multivitamins had an effect on total white blood cell count. *Wafaie W Fawzi, Gernard I Msamanga, David J Hunter Department of Nutrition, Harvard School of Public Health, Boston, MA 02115, USA 1
2
3
4
Bureau of Statistics [Tanzania] and Macro International. Tanzania demographic and health survey, 1996. Calverton, Maryland: Bureau of Statistics and Macro International, 1997: 107. Statistical Department [Uganda] and Macro International. Uganda Demographic and Health Survey, 1994. Calverton, Maryland: Statistics Department [Uganda] and Macro International, 1996: 107. Central Statistical Office [Zambia] and Ministry of Health and Macro International. Zambia demographic and health survey, 1996. Calverton, Maryland: Central Statistical Office and Macro International, 1997: 105. Central Statistical Office [Zimbabwe] and Macro International. Zimbabwe demographic and health survey, 1994. Calverton, Maryland: Central Statistical Office and Macro International, 1995: 109.
THE LANCET • Vol 352 • August 22, 1998
Wernicke’s encephalopathy Sir—Andrea Gropman and colleagues (June 6, 1704)1 could have emphasised the important lesson of the dangers of intravenous glucose in states of severe thiamine depletion. The causes of Wernicke’s encephalopathy and the hazards of intravenous glucose are well documented, but the lesson continues to be forgotten. I report an associated case from general practice to highlight the dangers and perceived dangers of treatment of Wenicke’s encephalopathy. A 60-year old malnourished woman with a previous diagnosis of ulcerative colitis was seen at home because her husband was concerned about her slurred speech, weakness, and odd eye movements. On examination she had dysarthria, fluctuating consciousness, dysconjugate eye movements, and unrecordable blood pressure. Wernicke’s encephalopathy was diagnosed, and she was referred to hospital with that diagnosis and the suggestion that she be given thiamine before intravenous glucose. The next day, her husband reported her deterioration on treatment, and she was transferred to an institution for haemodialysis, and later to a neurological institution for subsequent management of a presumed metabolic encephalopthy which required a gastrostomy and long convalescence. Subsequent inquiry revealed that a glucose-containing intravenous infusion had been set up on arrival at the first institution, and that thiamine was ordered but was unavailable, although the pharmacy had provided an intravenous thiamine-containing multivitamin preparation, Pabrinex. The attending physicians were aware that there was a possibility of anaphylactic reactions with intravenous thiamine and decided to forgo use of Pabrinex. Data on file held by the makers of Pabrinex suggest that only about 40 cases of such reactions have been reported despite millions of doses of the preparation having been used. Thiamine and transketolase assay is routinely available only at two centres in the UK and neither assay is rapid. In the case reported by Gropmans and colleagues, the thiamine assay was sent to another institution (personal communication). The lesson of Gropmans’ case and the one I report here is that once the clinical diaganosis of Wernicke’s encephalopathy is suspected, appropriate treatment should be given before awaiting an assay result so that
the patient’s life is not threatened. M G Bamber The Surgery, Back Lane, Colsterworth, Grantham, Lincs NG33 5NJ, UK. 1
Gropman AL, Gaillard WD, Campbell P, Charya SV. Wernicke’s encephalopathy due to self-starvation in a child. Lancet 1998; 351: 1704–05.
Evidence on vitamin B6 questioned Sir—Katharina Dalton and Michael Dalton (July 4, p 62)1 claim that vitamin B6 causes long-term health damage,1 backing up their extended report to the Agriculture Select Committee.2 The limited data given in the main report, coupled with the data from the original study,3 which claimed that B6 produced symptoms of a neurotoxic syndrome, provide a rather uncertain history of the women’s samples studied by the Daltons (table). The Daltons’ conclusions1,2 are fatally flawed by the fact that in a treatment versus control design, the two groups should differ only in respect of the factor under consideration. The use of the word control is a total misnomer. The population of patients who might have been used as controls is inaccessible to the sampler. Those taken as controls were alive in 1996; sufficiently ill in 1996 to require a consultation; not taking B6 in 1984; but sufficiently ill in 1984 to warrant a blood test. The Daltons claim that the controls were age matched, yet there are 102 in the treatment group and 98 theoretical controls. The loss of between 40–50% of each sample, and the fact that the control samples had had recent consultations with the Daltons, creates a further selfselection of controls which makes it impossible to see the samples as representative of those who take B6 and those who do not. No attempt is made to compare earlier evidence on the attrition samples with similar evidence on the responding samples. With such a flawed study there is little point in looking at comparative figures. There are also other forms of missing evidence that could bias the results in either direction. No evidence is offered on the pre-1984 history of illness or treatment in each sample. No evidence is offered on the socioeducational background and age distribution of the women in each sample. No evidence is offered on the nutritional quality of the diets of those sampled. No evidence is offered on the use of oral contraceptives within each sample, despite the many
655
small-for-gestational-age babies. Second, the comparability of the two groups during pregnancy is not described, and possible differences might have occurred despite randomisation, especially in a factorial design. Third, the reported compliance of 91% is very high for a trial with 4 months of treatment in an African population, but no objective information was presented about a possible difference of compliance between the group of women who received multivitamins and the group who did not. Women receiving multivitamins may have rapidly felt in better shape (especially for vitamin C supplementation), and their compliance could have been better than in the group who did not receive this intervention, in which there were women receiving vitamin A alone. Moreover, we have no details of the maternal characteristics at the beginning and end of pregnancy: some that could affect pregnancy outcome, such as maternal body weight gain or other clinical indices, and be improved by multivitamin supplementation, could have reduced the power to detect a difference in the vitamin A comparison. We also have reservations about the feasibility of such an intervention early in pregnancy since most African women use prenatal services late in pregnancy.2 In this Tanzanian trial setting, the selection process of eligible women and the characteristics of women enrolled could have partly accounted for some of the positive results—eg, high HIV-1 screening and trial acceptability, or high drug compliance. Finally, Fawzi and co-workers offer reasons for the absence of beneficial effects of vitamin A supplementation. However, the essential objective of their trial has not yet been achieved— namely, a benefit of vitamin A supplementation on maternal and infant morbidity, as has already been suggested in other such trials.3,4 We, as are many researchers in prevention of vertical transmission of HIV-1 in developing countries,5 are pleased to hear about the potential benefit effect of multivitamin supplementation but are waiting for information on the association between vitamin A supplementation and evolution of women’s health, HIV-1 mother-tochild transmission, and child morbidity. *Katia Castetbon, Valériane Leroy, François Dabis INSERM U330, Université Victor SegalenBordeaux 2, 33 076 Bordeaux, France
654
1
2
3
4
5
Fawzi WW, Msamanga GI, Speigelman D, et al. Randomised trial of effects of vitamin supplements on pregnancy outcomes and T cell counts in HIV-1-infected women in Tanzania. Lancet 1998; 351: 1477–82. Mtimavalye L, Biggar RJ, Taha TE, Chiphangwi J. Maternal-infant transmission of HIV-1. N Engl J Med 1995; 332: 890–91. Coutsoudis A, Bobat RA, Coovadia HM, Kuhn L, Tsai WY, Stein ZA. The effects of vitamin A supplementation on the morbidity of children born to HIV-infected women. Am J Publ Hlth 1995; 85: 1076–81. Coutsoudis A, Moodley D, Pillay K, et al. Effects of vitamin A supplementation on viral load in HIV-1-infected pregnant women. J Acquir Immune Defic Syndr Hum Retrovirol 1997; 15: 86–87. Dabis F, Msellati P, Newell ML, et al. Methodology of intervention trials to reduce mother to child transmission of HIV with special reference to developing countries. AIDS 1995; 9 (suppl A): S67–74.
Sir—Wafaie Fawzi and colleagues’ results1 bring potent arguments for the use of vitamin supplements to reduce adverse pregnancy outcome in African HIV-1 infected women. Data and interpretation of the effect of vitamins on T-cell counts, however, raise questions that should be addressed before such an intervention is applied. Can the mechanism by which vitamins increase CD4 cell counts slow the process of HIV disease progression? It is well known that HIV-induced alterations are distinct according to the T cell subsets, mainly including a concomitant rise in CD8 activated T cells and a fall in CD4 cells, this last event being a multifactorial process. Peripheral cell loss results from decreased proliferation, increased cell death by apoptosis, increased emigration to lymph nodes, and, but this last mechanism is controversial, reduced central T cell production.2 The global rise noted by Fawzi and co-workers in all peripheral mature T subsets, rather than in CD4 cells alone, suggests an impact on the last process—ie, proliferation of leucocyte progenitors.3 Data on total white blood cells, differential white cell counts, total lymphocyte counts (which are often proposed as an alternative to CD4 counts in the African setting4), and CD4/CD8 ratio should be discussed. A trophic effect on both fetal cells and haematological precursors, rather than a real immunological T cell improvement, could well result from the use of folic acid and vitamin B12, micronutrients which have key roles in the metabolism of proliferating cells. Is the increase seen in CD4 cells, resulting from this whole T lymphocyte population enlargement, protective against opportunistic diseases? The value of absolute CD4 cell count as a surrogate marker of
progression to AIDS has been confirmed in a prospective study. 5 Nevertheless, this fact does not anticipate the functional value of expanded CD4 cells during treatment. In fact, the relation between the gain in CD4 and the protection against pathogens in treated patients is being intensively researched. Could generalisation of multivitamin supplementation in HIVinfected people have adverse effects? Although an increase in viral load is not likely to occur, this load should be monitored. Alternatively, a theoretical risk of some protozoal opportunistic diseases such as toxoplasmosis should result from the widespread use of folate supplementation. Indeed, this risk could undermine folic acid antagonists administration, one of the rare weapons for the prevention of AIDS in developing countries.4 Eric Ledru Viral Oncology Unit, Pasteur Institute, 75724 Paris, France (e-mail: [email protected]) 1
2
3
4
5
Fawzi WW, Msamanga GI, Spiegelman D, et al. Randomised trial of effects of vitamin supplements on pregnancy outcomes and T cell counts in HIV-1-infected women in Tanzania. Lancet 1998; 351: 1477–82. Rosenberg YJ, Anderson AO, Pabst R. HIV-induced decline in blood CD4/CD8 ratios: viral killing or altered lymphocyte trafficking? Immunol Today 1998; 19: 10–17. Beutler E, Lichtman MA, Coller BS, Kippl TJ. Williams hematology, fifth ed. New York: McGraw-Hill, 1995. Ledru E, Diagbouga S, Meda N, et al. A proposal for basic management of HIV disease in West-Africa. Use of clinical staging and haemogram data. Int J STD AIDS (in press). Perneger TV, Yerly S, Perrin L. Transforming laboratory test results to improve clinical outcome predictors in HIV patients. J Acq Immun Defic Syndr Hum Retroviral 1998; 17: 442–49.
Authors’ reply Sir—We agree with Katia Castetbon and colleagues that we have limited power to detect small effects of vitamin A on adverse pregnancy outcomes. We also stated that the confidence intervals of our results are compatible with a modest protective assocation of vitamin A, although it was smaller than the effect of multivitamins and was not statistically significant. In addition, we reported that there were no significant differences between treatment arms in various baseline characteristics. There were also no differences in compliance between treatment arms, as measured by pill counts of supplements or ingestion of the vitamin A dose at delivery. Women who received vitamin A supplements had significant
THE LANCET • Vol 352 • August 22, 1998
CORRESPONDENCE
improvements in serum vitamin A concentrations compared with those who did not. The effect of vitamin A was unlikely to be obscured by possible effects of multivitamins on maternal weight or clinical stage of disease. The effects of vitamin A or multivitamins were not modified by baseline body mass index or CD 4 cell counts. Furthermore, there was no interaction between the effect of vitamin A and that of multivitamins without vitamin A on adverse pregnancy outcomes or on maternal T cell counts. Our findings are generalisable to women who present to prenatal care during the second trimester. In our Tanzanian study, the median gestation age at enrolment was 5·3 months. This time is similar to the median gestation age at presentation to antenatal services among women in the general population who participated in the demographic and health surveys of Tanzania (5·6 months), 1 Uganda (5·9),2 Zambia (5·6),3 and Zimbabwe (5·1).4 Thus, we believe that provision of vitamin supplements from the fifth month of pregnancy is potentially feasible. We agree with Eric Ledru that it is important to assess both the efficacy and any potential adverse effects of the multivitamin supplements on progression of HIV disease and the risk of opportunistic infections. We are examining the effect of both treatments on these endpoints and on vertical transmission and infant mortality. Similar to the effects of CD4 and CD8 cell counts, multivitamins but not vitamin A resulted in an improvement in CD4/CD8 ratio. Neither vitamin A nor multivitamins had an effect on total white blood cell count. *Wafaie W Fawzi, Gernard I Msamanga, David J Hunter Department of Nutrition, Harvard School of Public Health, Boston, MA 02115, USA 1
2
3
4
Bureau of Statistics [Tanzania] and Macro International. Tanzania demographic and health survey, 1996. Calverton, Maryland: Bureau of Statistics and Macro International, 1997: 107. Statistical Department [Uganda] and Macro International. Uganda Demographic and Health Survey, 1994. Calverton, Maryland: Statistics Department [Uganda] and Macro International, 1996: 107. Central Statistical Office [Zambia] and Ministry of Health and Macro International. Zambia demographic and health survey, 1996. Calverton, Maryland: Central Statistical Office and Macro International, 1997: 105. Central Statistical Office [Zimbabwe] and Macro International. Zimbabwe demographic and health survey, 1994. Calverton, Maryland: Central Statistical Office and Macro International, 1995: 109.
THE LANCET • Vol 352 • August 22, 1998
Wernicke’s encephalopathy Sir—Andrea Gropman and colleagues (June 6, 1704)1 could have emphasised the important lesson of the dangers of intravenous glucose in states of severe thiamine depletion. The causes of Wernicke’s encephalopathy and the hazards of intravenous glucose are well documented, but the lesson continues to be forgotten. I report an associated case from general practice to highlight the dangers and perceived dangers of treatment of Wenicke’s encephalopathy. A 60-year old malnourished woman with a previous diagnosis of ulcerative colitis was seen at home because her husband was concerned about her slurred speech, weakness, and odd eye movements. On examination she had dysarthria, fluctuating consciousness, dysconjugate eye movements, and unrecordable blood pressure. Wernicke’s encephalopathy was diagnosed, and she was referred to hospital with that diagnosis and the suggestion that she be given thiamine before intravenous glucose. The next day, her husband reported her deterioration on treatment, and she was transferred to an institution for haemodialysis, and later to a neurological institution for subsequent management of a presumed metabolic encephalopthy which required a gastrostomy and long convalescence. Subsequent inquiry revealed that a glucose-containing intravenous infusion had been set up on arrival at the first institution, and that thiamine was ordered but was unavailable, although the pharmacy had provided an intravenous thiamine-containing multivitamin preparation, Pabrinex. The attending physicians were aware that there was a possibility of anaphylactic reactions with intravenous thiamine and decided to forgo use of Pabrinex. Data on file held by the makers of Pabrinex suggest that only about 40 cases of such reactions have been reported despite millions of doses of the preparation having been used. Thiamine and transketolase assay is routinely available only at two centres in the UK and neither assay is rapid. In the case reported by Gropmans and colleagues, the thiamine assay was sent to another institution (personal communication). The lesson of Gropmans’ case and the one I report here is that once the clinical diaganosis of Wernicke’s encephalopathy is suspected, appropriate treatment should be given before awaiting an assay result so that
the patient’s life is not threatened. M G Bamber The Surgery, Back Lane, Colsterworth, Grantham, Lincs NG33 5NJ, UK. 1
Gropman AL, Gaillard WD, Campbell P, Charya SV. Wernicke’s encephalopathy due to self-starvation in a child. Lancet 1998; 351: 1704–05.
Evidence on vitamin B6 questioned Sir—Katharina Dalton and Michael Dalton (July 4, p 62)1 claim that vitamin B6 causes long-term health damage,1 backing up their extended report to the Agriculture Select Committee.2 The limited data given in the main report, coupled with the data from the original study,3 which claimed that B6 produced symptoms of a neurotoxic syndrome, provide a rather uncertain history of the women’s samples studied by the Daltons (table). The Daltons’ conclusions1,2 are fatally flawed by the fact that in a treatment versus control design, the two groups should differ only in respect of the factor under consideration. The use of the word control is a total misnomer. The population of patients who might have been used as controls is inaccessible to the sampler. Those taken as controls were alive in 1996; sufficiently ill in 1996 to require a consultation; not taking B6 in 1984; but sufficiently ill in 1984 to warrant a blood test. The Daltons claim that the controls were age matched, yet there are 102 in the treatment group and 98 theoretical controls. The loss of between 40–50% of each sample, and the fact that the control samples had had recent consultations with the Daltons, creates a further selfselection of controls which makes it impossible to see the samples as representative of those who take B6 and those who do not. No attempt is made to compare earlier evidence on the attrition samples with similar evidence on the responding samples. With such a flawed study there is little point in looking at comparative figures. There are also other forms of missing evidence that could bias the results in either direction. No evidence is offered on the pre-1984 history of illness or treatment in each sample. No evidence is offered on the socioeducational background and age distribution of the women in each sample. No evidence is offered on the nutritional quality of the diets of those sampled. No evidence is offered on the use of oral contraceptives within each sample, despite the many
655