Iron status and cardiovascular disease risk in black South African women: the PURE study

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1 Iron sttus nd crdiovsculr disese risk in blck South Africn women: the PURE study Aderibigbe OR, MSc, Pis PT, PhD, Mmbolo RL, PhD, Kruger HS, PhD, Vorster HH, DSc, b Kruger A, PhD Centre of Excellence for Nutrition nd b Afric Unit for Trnsdisciplinry Helth Reserch, North-West University, Potchefstroom Correspondence to: Olide R Aderibigbe, e-mil: connecttolide@yhoo.com Keywords: iron sttus, crdiovsculr disese, Africn women, PURE study Abstrct Objective: To exmine the ssocitions between mesures of iron sttus nd crdiovsculr disese (CVD) risk fctors in South Africn women. Method: In cross-sectionl study, demogrphic informtion nd helth history were obtined during individul interviews using vlidted questionnires in the North West Province, South Afric. Anthropometric indices, iron indices, blood pressure, blood glucose nd lipid profiles were mesured using stndrd procedures in pprently helthy blck South Africn women ged 35 yers or older. Iron sttus ws ssessed using serum concentrtions of ferritin, trnsferrin receptor (TfR) nd TfR:ferritin rtio. Results: Associtions between iron sttus prmeters nd CVD risk fctors were generlly wek (r < 0.3, p < 0.01) nd were not retined when djustment ws mde for ge, body mss index, smoking, lcohol consumption nd C-rective protein in the nlysis. Wist circumference (WC) nd wist:hip rtio (WHR) were higher in the fourth qurtile of serum ferritin thn in the third qurtile, nd lso in the third qurtile compred to the second qurtile (P < 0.05). Bsed on WC nd WHR respectively, 31% nd 52% of the women hd excess bdominl obesity. The men (95% confidence intervl) serum TfR concentrtion ws high, t 9.09 µg/ml (8.77, 9.44), indicting risk of iron deficiency. The men (95% confidence intervl) concentrtions of lipids [totl cholesterol 4.78 mmol/l (4.64, 4.93), high-density lipoprotein cholesterol 1.45 mmol/l (1.39, 1.52), low-density lipoprotein cholesterol 1.65 mmol/l (1.53, 1.78), triglyceride 1.12 mmol/l (1.07, 1.18)] were within reference rnges. Conclusion: No significnt ssocition ws found between iron sttus prmeters nd estblished CVD risk fctors. However, excessive bdominl diposity indicted by high WC nd WHR contributes significntly to incresed serum ferritin concentrtion in this popultion. Peer reviewed. (Submitted: Accepted: ) SAJCN : Introduction The role tht iron plys in the pthogenesis of crdiovsculr disese (CVD) hs incresingly been of interest in the field of public helth. Excess iron hs been proposed to ctlyse the conversion of poorly rective free rdicls into highly rective ones, process known to predispose to or promote the incidence of CVD. 1 At the moment, number of iron supplementtion or fortifiction progrmmes re ongoing in mny developed nd developing ntions. Reports 2 hve shown tht the percentge of iron-replete persons is on the increse in developed ntions; reports lso exist of iron overlod in subgroups of people in the less developed ntions. 3 Moreover, there re specultions tht iron overlod my become world epidemic. 4 Most of the cross-sectionl studies tht exmined the link between iron stores nd incresed CVD risk were conducted in men In study in women with poor iron sttus, strong positive ssocition ws found between iron stores nd CVD risk fctors. 2 This rises concern bout the sitution mong Africn women. While undernutrition remins problem, obesity nd ssocited noncommunicble diseses, which were thought to be problem of industrilised countries, re now incresingly becoming prevlent in the less industrilised countries, especilly those undergoing trnsition It hs been proposed tht iron overlod my not be problem in helthy popultion, but tht in persons with incresed oxidtive stress nd obesity, iron overlod my pose greter risk However, studies tht hve exmined the role of iron sttus in CVD hve been inconsistent, possibly becuse of the use of different mesures of iron sttus. 5-6,10-11 Iron sttus mesured s dietry iron, serum iron, serum ferritin nd trnsferrin sturtion hs limittions becuse these re influenced by short-term effects such s inflmmtion, iron intke, blood loss nd diurnl vritions Soluble trnsferrin receptor (TfR) concentrtion hs been suggested s n improved mesure of iron sttus. 18 Furthermore, becuse serum ferritin reflects the storge iron comprtment nd serum TfR reflects the functionl iron comprtment, the TfR:ferritin rtio hs been suggested s better estimte of body iron compred to either 179

2 of the two mesured independently. 19 Tuominen et l 8 reported tht this rtio is virtully independent of inflmmtion. In view of this, the present study ws imed t using concentrtions of serum ferritin, TfR nd TfR:ferritin rtio to exmine the ssocition between iron sttus nd CVD risk fctors. Method Study design, subject selection nd orgnistionl procedures This cross-sectionl study ws prt of the North West province, South Afric (NWPSA) leg of the 12-yer Prospective Urbn nd Rurl Epidemiologicl (PURE) study. It investigted the effect of helth trnsition on chronic diseses of lifestyle in urbn nd rurl subjects. All the bseline dt used for the present study were collected during 2005 in the North West. Migrtion stbility ws the min selection criterion within the chosen rurl nd urbn communities. The rurl community (A) ws identified 450 km west of Potchefstroom, on the highwy to Botswn. A deep rurl community (B), 35 km est from A nd only ccessible vi grvel rod, ws lso included. Community C ws selected from the estblished prt of the township next to Potchefstroom, nd community D ws selected from the informl settlements surrounding community C. A household census regrding number of people, their ges nd helth profile ws rndomly done in houses (1 500 in ech community). The hed of ech household gve signed consent to complete the questionnire. If person refused or ws not t home, the next house ws tken nd non-complier questionnire ws completed. From the dt obtined, pper selection of possible subjects with no reported chronic diseses of lifestyle, tuberculosis or dignosed humn immunodeficiency virus (HIV) infection ws mde. A totl of (35 yers nd older) pprently helthy blck Africn volunteers were recruited. The smple for the study described in this rticle consisted of only the femle prticipnts. Dt collection ws divided into sttions. Sttion 1 involved the dministrtion of questionnires, sttion 2 involved nthropometric mesurements nd blood pressure (BP) mesurements, nd sttion 3 involved blood collection. Prticipnts were fsted (10 12 hours) for the bseline blood smpling nd other mesurements. Trined field workers ssisted in providing informtion to the prticipnts in their lnguge of choice. Prticipnts received feedbck regrding their BP, fsting blood glucose concentrtions nd HIV sttus nd were referred to counselling services, clinics or hospitls where necessry. Trvel expenses of prticipnts were covered. Ethicl pprovl ws obtined from the Ethics Committee of the North-West University, Potchefstroom, South Afric (ethics number: 04M10), nd signed informed consent forms were obtined from ll prticipnts. Permission to conduct the study ws given by the North West Deprtment of Helth, tribl chiefs, community leders, employers nd myors. Questionnires Structured, vlidted demogrphic, socio-economic nd lifestyle questionnires were dministered by trined field workers during home visits in the lnguge preferred by the prticipnts. Adpted questionnires were used by ll countries prticipting in the PURE study. Anthropometric mesurements Anthropometric mesurements were crried out by biokineticists. Height ws mesured to the nerest 0.5 cm with stdiometer (Invict, IP 1465, United Kingdom), nd weight ws determined on portble electronic scles to the nerest 0.01 kg (Precision Helth Scle, A & D Compny, Jpn). All the mesurements were conducted ccording to the guidelines dopted t the Ntionl Institute of Helthsponsored Arlie Conference. 20 Body circumferences of prticipnts were mesured in light underwer with clibrted instruments (Holtin unstretchble metl tpe, John Bull clipers). Body mss index (BMI) ws clculted by dividing weight in kilogrms by height in metres squred. Wist:hip rtio (WHR) ws clculted by dividing wist circumference (WC) by hip circumference in centimetres. HIV sttus Everyone who signed n informed consent form ws tested for HIV infection, but ws given the choice of knowing her sttus. Whole blood ws used for the determintion of HIV sttus with the First Response (PMC Medicl, Indi) rpid HIV crd test. If tested positive, the test ws repeted with the Preeshk (BHAT Biotech Indi) crd test. Pre-test counselling ws done in groups of 10 persons before the blood smple ws tken, nd individul posttest counselling ws done ccording to the protocol of the Ntionl Deprtment of Helth of South Afric. 21 Blood, serum nd plsm smples A disposble needle ws used to drw blood from the ntecubitl vein in the right rms of prticipnts. The blood collection tubes were ppropritely filled in order to ensure optiml blood-to-nticogulnt rtios. Ech tube ws inverted gently five times for thorough mixing. Smples were plced in ice boxes fter proper lbelling. A new sterile-trnsfer pipette ws used for liquotting blood smples for nlysis. Serum ws prepred by llowing blood to clot t room temperture for 30 minutes; it ws then centrifuged t g for 15 minutes t 10 C. Blood ws centrifuged within two hours of collection. All blood nd serum smples were stored t -70 C in the lbortory. Plsm smples were collected in ethylenediminetetrcetic cid (EDTA) tubes, centrifuged t g for 15 minutes t 4 C nd trnsferred to cryo tubes for storge t -70 C. Biochemicl nd physiologicl nlyses Systolic BP nd distolic BP were mesured with the vlidted OMRON HEM-757 device (Omron HEM-757). After 10-minute rest period, BP mesurements were performed twice (five minutes prt) on the right rm (brchil rtery), while the prticipnts were seted upright nd relxed with the right rm supported t hert level. Plsm glucose ws mesured using Vitros DT6011 Chemistry Anlyser, n Ortho-Clinicl Dignostics tool (Rochester, New York, United Sttes of Americ). Quntittive determintion of totl cholesterol (TC), highdensity lipoprotein cholesterol (HDL-C), triglyceride (TG) nd highsensitivity C-rective protein (CRP) concentrtion in serum ws done by Sequentil Multiple Anlyser Computer (SMAC) using the Konelb 20i uto nlyser (Thermo Fisher Scientific Oy, Vnt, Finlnd). Low-density lipoprotein cholesterol (LDL-C) ws clculted using the Friedewld formul. 22 Serum ferritin nd TfR concentrtions were determined quntittively using n enzyme immunossy procedure 180

3 (Rmco Lbortories, Inc, Stfford Texs). The coefficient of vrince (CV) for ll ssys ws less thn 10%. Sttisticl nlysis Dt were nlysed using version 17 of the Sttisticl Pckge for Socil Sciences (SPSS Inc Chicgo III, September 2008). Dt were not normlly distributed nd were log trnsformed to improve normlity. Dt were presented s men [95% confidence intervl (CI)]. Person correltion ws used to ssess the ssocitions between iron sttus prmeters nd CVD risk fctors. In this study, the following CVD risk fctors were exmined: BMI, WC, WHR, TC, LDL-C, HDL-C, TG, systolic nd distolic BP, plsm glucose nd CRP. Age, BMI, smoking, lcohol consumption nd serum CRP were treted s vlid confounders. Assocition ws further ssessed by prtil correltion, djusting for these confounders. For further ssessment of the reltionship between iron sttus nd CVD risk fctors, prticipnts were grouped nd nlysed in qurtiles of ferritin, TfR nd TfR:ferritin rtio. Multivrite nlysis ws used to ssess significnt differences between different qurtiles before nd fter djusting for vlid confounders. A P < 0.05 ws considered sttisticlly significnt. HIV sttus did not confound or modify the ssocitions between iron indices nd CVD risk fctors; hence, it ws not treted s vlid confounder. Tble I: Selected chrcteristics of women prticipnts in the PURE study (n = 1 262) Vrible Men (95% confidence intervl) Age (yers) (48.57, 49.76) Smoking sttus (cigrettes/dy) 2.61 (2.38, 2.85) Alcohol consumption (g/dy) 7.74 (6.59, 8.89) Body mss index (kg/m 2 ) (23.22, 24.54) Wist circumference (cm) (75.16, 77.80) Wist:hip rtio 0.80 (0.79, 1.81) TfR (µg/ml) 9.09 (8.77, 9.44) Ferritin (µg/l) (81.84, ) TfR:ferritin rtio 0.25 (0.19, 0.30) Totl cholesterol (mmol/l) 4.78 (4.64, 4.93) High density lipoprotein cholesterol (mmol/l) 1.45 (1.39, 1.52) Triglyceride (mmol/l) 1.12 (1.07, 1.18) Low density lipoprotein cholesterol (mmol/l) 1.65 (1.53, 1.78) Distolic blood pressure blood pressure (84.52, 87.49) (mmhg) Systolic blood pressure blood pressure (mmhg) (125.60, ) Glucose (mmol/l) 5.34 (5.21, 5.47) C-rective protein (mg/l) 2.81 (1.84, 3.98) Tble II illustrtes the proportion (%) of women ccording to stndrd cutoff points for vribles nd the proportion of self-reported smokers nd lcohol consumers. Hlf (50%) of the prticipnts were selfreported smokers while 33% were lcohol consumers. In ddition, 53% were either overweight or obese (>25 kg/m 2 ), while 31% hd excess WC ( 88 cm) nd 52% hd excess WHR ( 0.80). As for iron indices, 56% hd high TfR concentrtion (> 8.5 µg/ml) while 33% hd excess iron stores s defined by ferritin concentrtion (> 150 µg/l). Those t risk s defined by incresed biologicl helth mrkers were 48% for TC, 27% for LDL-C, 23% for TG, 27% for glucose, 25% for CRP nd 43% for HDL-C. Distolic BP nd systolic BP were incresed in 57% nd 49% of the women respectively. Tble II: Proportion of women prticipnts in the PURE study ccording to stndrd cutoff points, smoking nd lcohol consumption sttus Vrible Recommended reference vlue n (%) Smokers Non-smokers Alcohol consumers Alcohol non-consumers Body mss index 23 < 18 kg/m kg/m 2 25 kg/m 2 Wist circumference 23 < 88 cm 88 cm Wist:hip rtio 23 < TfR 24 Ferritin 25 Totl cholesterol 26 High-density lipoprotein cholesterol 26 Triglyceride 26 Low-density lipoprotein cholesterol 26 Distolic blood pressure 26 Systolic blood pressure 26 Glucose 26 C-rective protein 27 < 8.5 µg/ml 8.5 µg/ml < 12 µg/l µg/l > 150 µg/l) 5 mmol/l > 5 mmol/l 1.3 mmol/l < 1.3 mmol/l 1.7 mmol/l > 1.7 mmol/l 3.0 mmol/l > 3.0 mmol/l 85 mmhg > 85 mmhg 130 mmhg > 130 mmhg 6.1 mmol/l > 6.1 mmol/l 10 mg/l > 10 mg/l 437 (50%) 430 (50%) 391 (33%) 787 (67%) 137 (12%) 410 (35%) 641 (53%) 808 (69%) 368 (31%) 534 (48%) 578 (52%) 462 (44%) 597 (56%) 94 (9%) 610 (58%) 355 (33%) 612 (52%) 564 (48%) 666 (57%) 506 (43%) 904 (77%) 265 (23%) 754 (73%) 281 (27%) 501 (43%) 670 (57%) 593 (51%) 578 (49%) 851 (73%) 316 (27%) 874 (75%) 296 (25%) Results Tble I outlines selected chrcteristics of women prticipnts in the PURE study. The men vlues of vribles were within recommended reference rnges, except for TfR nd WHR, which were higher, indicting risk for iron deficiency nd bdominl obesity respectively in this popultion. The correltions between iron indices nd CVD risk fctors re shown in Tble III. Ferritin correlted positively with TC, HDL-C, LDL-C, TG, distolic BP, systolic BP, CRP nd lcohol consumption before djusting for vlid confounders (ge, BMI, smoking, lcohol consumption nd CRP), but the correltions were not retined fter djustment. There ws negtive correltion between TfR nd 181

4 LDL-C, nd TG nd lcohol consumption. A positive correltion ws found between TfR nd WHR. All of these disppered fter djusting for vlid confounders. TfR:ferritin rtio correlted negtively with TC, LDL-C, TG, distolic BP, systolic BP, CRP nd lcohol consumption before djusting for vlid confounders, but ws not retined fter djustment. The correltions observed between iron indices nd CVD risk fctors were generlly wek (r < 0.3). CVD risk fctors re compred ccording to ferritin qurtiles in Tble IV. BMI nd WC were higher in qurtile three thn in qurtile one before djusting for vlid confounders. After djusting for the vlid confounders, WC in the third qurtile remined significntly higher thn in the second nd fourth qurtiles. WHR incresed cross ferritin qurtiles before djusting for vlid confounders. After djustment for vlid confounders, the increse from qurtile two to qurtile four remined significnt. TC, TG, LDL-C, distolic BP nd systolic BP were significntly higher in the fourth qurtile thn in the first two qurtiles before djusting for vlid confounders, but were not retined fter djustment. A significntly higher HDL-C vlue ws observed in qurtile four thn in qurtile one before djusting for confounders. No significnt difference ws observed for blood glucose cross ferritin qurtiles. CRP ws higher in qurtiles two, three nd four thn in qurtile one. Tble V shows the comprison of CVD risk fctors ccording to TfR qurtiles. BMI, WC, HDL-C, systolic BP, glucose nd CRP did not vry significntly mong the qurtiles. WHR ws significntly higher in qurtiles three nd four thn in qurtile two before djusting for ge, BMI, smoking, lcohol consumption nd CRP. In ddition, WHR ws higher in qurtile two thn in qurtile one before djusting for Tble III: Correltions between iron indices nd crdiovsculr disese risk fctors of prticipnts Ferritin (µg/l) TfR (µg/ml) TfR:ferritin rtio Vribles r b r p r r p r r p Ferritin (µg/l) c c c TfR (µg/ml) c c.410 c TfR:ferritin rtio c c.511 c.410 c Body mss index (kg/m 2 ) Wist circumference (cm) Wist:hip rtio c Totl cholesterol (mmol/l).065 d d High density lipoprotein cholesterol (mmol/l).065 d Triglyceride (mmol/l).187 c d c Low density lipoprotein cholesterol (mmol/l) Distolic blood pressure (mmhg) Systolic blood pressure (mmhg).140 c d c c c c c Glucose (mmol/l) C-rective protein (mg/l).158 c c -- Smoking (cigrette/dy) Alcohol consumption (g/dy).207 c d c -- = Person correltion coefficient fter djusting for ge, body mss index, smoking, lcohol consumption nd C-rective protein, b = prtil correltion coefficient fter djusting for ge, body mss index, smoking, lcohol consumption nd C-rective protei, c = Correltion is significnt t the 0.01 level (two-tiled), d = Correltion is significnt t the 0.05 level (two-tiled) Tble IV: Men (95% confidence intervl) of CVD risk fctors ccording to ferritin qurtiles Vribles Qurtile 1 Ferritin < 38.2µg/l n = 277 Qurtile 2 Ferritin µg/l n = 272 Qurtile 3 Ferritin µg/l n = 251 Qurtile 4 Ferritin > 208.2µg/l n = 260 Men (95% CI) Men (95% CI) Men (95% CI) Men (95% CI) Body mss index (kg/m 2 ) (24.72, 26.36) (25.24, 26.92) (26.24, 28.05) 24.09,b,c (23.33, 24.89) Wist circumference (cm) (77.09, 80.35) (77.80, 81.09) 82.03,b,d,e (80-35, 83.75) 79.06c f (77.45, 80.72) Wist:hip rtio 0.78 (0.77, 0.79) 0.79 (77.80, 81.09) 0.80,e (0.79, 0.82) 0.82,b,c,f (0.81, 0.83) Totl cholesterol (mmol/l) 4.86 (4.69, 5.04) 4.88 (4.73, 5.06) 5.05 (4.89, 5.24) 5.15,b (4.98, 5.33) High density lipoprotein cholesterol (mmol/l) 1.39 (1.31, 1.46) 1.41 (1.33, 1.48) 1.40 (1.32, 1.48) 1.51 (1.43, 1.58) Triglyceride (mmol/l) 1.05 (0.99, 1.12) 1.13 (1.07, 1.21) 1.28,b (1.20, 1.36) 1.33,b (1.25, 1.41) Low density lipoprotein cholesterol (mmol/l) 1.63 (1.49, 1.79) 1.76 (1.61, 1.93) 2.06,b (1.87, 2.26) 2.13,b (1.95, 2.34) Distolic blood pressure (mmhg) (81.47, 84.72) (85.11, 88.71) (86.29, 89.94) 90.36,b (1.95, 2.34) Systolic blood pressure (mmhg) (122.74, ) (127.93, ) (130.31, ) ,b (133.96, ) Glucose (mmol/l) 5.39 (5.23, 5.55) 5.49 (5.33, 5.66) 5.52 (5.34, 5.70) 5.49 (5.33, 5.66) C-rective protein (mg/l) 2.36 (1.96, 4.18) 3.47 (1.96, 4.18) 3.81 (3.13; 4.62) 3.94 (3.26, 4.76) P < 0.05 significntly different from qurtile 1 (undjusted) b P < 0.05 significntly different from qurtile 2 (undjusted) c P < 0.05 significntly different from qurtile 3 (undjusted) d P < 0.05 sinificntly different from qurtile 1 (djusted for ge, body mss index, smoking, lcohol consumption nd C-rective protein) e P < 0.05 significntly different from qurtile 2 (djusted for ge, body mss index, smoking, lcohol consumption nd C-rective protein) f P < 0.05 significntly different from qurtile 3 (djusted for ge, body mss index, smoking, lcohol consumption nd C-rective protein) 182

5 Tble V: Men (95% confidence intervl) of CVD risk fctors ccording to TfR qurtiles Vribles Qurtile 1 TfR < 7.8 µg/l n = 374 Qurtile 2 TfR µg/l n = 262 Qurtile 3 TfR µg/l n = 216 Qurtile 4 TfR > 11.9 µg/l n = 208 Men (95% CI) Men (95% CI) Men (95% CI) Men (95% CI) Body mss index (kg/m 2 ) (24.60, 26.06) (24.94, 26.66) (24.88, 26.79) (25.00, 26.91) Wist circumference (cm) (77.98, 80.90) (77.80, 81.09) (78.16, 81.84) (78.88, 82.60) Wist:hip rtio 0.80 (0.79, 0.81) 0.78 (0.77, 0.79) 0.81 b (0.79, 0.81) 0.80 b (0.79, 0.81) Totl cholesterol (mmol/l) 5.04 (4.89, 5.19) 4.88 c (4.72, 5.05) 5.06 c (4.88, 5.27) 4.94 (4.75, 5.12) High density lipoprotein cholesterol (mmol/l) 1.42 (1.36, 1.48) 1.43 (1.34, 1.50) 1.46 (1.38, 1.55) 1.40 (1.32, 1.48) Triglyceride (mmol/l) 1.27 (1.21, 1.34) 1.13 (1.06, 1.20) 1.14 (1.07, 1.22) 1.19 (1.11, 1.27) Low density lipoprotein cholesterol (mmol/l) 2.05 (1.89, 2.22) 1.71 (1.56, 1.88) 1.84 (1.66, 2.04) 1.85 (1.67, 2.06) Distolic blood pressure (mmhg) (85.11, 88.10) (85.70, 89.33) (84.91, 88.92) 87.09,d (85.11, 89.12) Systolic blood pressure (mmhg) (129.12, ) (128.82, ) (128.82, ) (127.35, ) Glucose(mmol/l) 5.40 (5.26, 5.54) 5.49 (5.33, 5.66) 5.38 (5.19, 5.57) 5.66 (5.47, 5.86) C-rective protein (mg/l) 3.13 (2.66, 3.68) 3.29 (2.72, 3.98) 3.15 (5.19, 5.57) 3.89 (5.47, 5.86) P < 0.05 significntly different from qurtile 1 (undjusted) b P < 0.05 significntly different from qurtile 2 (undjusted) c P < 0.05 significntly different from qurtile 1 (djusted for ge, body mss index, smoking, lcohol consumption nd C-rective protein) d P < 0.05 significntly different from qurtile 2 (djusted for ge, body mss index, smoking, lcohol consumption nd C-rective protein) Tble VI: Men (95% confidence intervl) of CVD risk fctors ccording to TfR:ferritin rtio qurtiles Vribles Qurtile 1 TfR:ferritin < 0.04 n = 256 Qurtile 2 TfR:ferritin n = 263 Qurtile 3 TfR:ferritin n = 281 Qurtile 4 TfR:ferritin n = 281 Men (95% CI) Men (95% CI) Men (95% CI) Men (95% CI) Body mss index (kg/m 2 ) (23.33, 24.88) (26.06, 27.86) (25.35, 27.03) 25.52,c (24.66, 26.36) Wist circumference (cm) (77.44, 80.72) 81.65,b (79.98, 83.36) (77.98, 81.28) c (77.26, 80.72) Wist:hip rtio 0.82 (0.81, 0.83) 0.80 (0.79, 0.81) 0.79 (0.78, 0.80) 0.78 (0.78, 0.80) Totl cholesterol (mmol/l) 5.15 (4.97, 5.33) 4.97 (4.80, 5.15) 4.94 (4.78, 5.11) 4.88 (0.77, 0.80) High density lipoprotein cholesterol (mmol/l) 1.51 (1.44, 1.60) 1.39 (1.31, 1.46) 1.39 (1.32, 1.47) 1.40 (1.33, 1.48) Triglyceride (mmol/l) 1.37 (1.32, 1.46) 1.22 (1.31, 1.46) 1.14 (1.07, 1.21) 1.06,c (1.00, 1.13) Low density lipoprotein cholesterol (mmol/l) 2.18 (1.99, 2.40) 1.93 (1.75, 2.12) 1.79 (1.64, 1.97) 1.65,c (1.50, 1.81) Distolic blood pressure (mmhg) (88.30, 92.04) (86.29, 89.94) (84.91, 88.30) 83.36,c,d (81.65, 85.11) Systolic blood pressure (mmhg) (133.35, ) (86.29, 89.94) (128.23, ) ,c,d (122.74, ) Glucose (mmol/l) 5.53 (5.35, 5.70) 5.38 (5.22, 5.55) 5.52 (5.35, 5.68) 5.45 (5.28, 5.62) C-rective protein (mg/l) 3.87 (3.21, 4.68) 3.79 (3.13, 4.60) 3.40 (2.83, 4.09) 2.42,c,d (2.00, 2.92) P < 0.05 significntly different from qurtile 1 (undjusted) b P < 0.05 significntly different from qurtile 1 (djusted for ge, body mss index,smoking, lcohol consumption nd C-rective protein) c P < 0.05 significntly different from qurtile 2 (undjusted) d P < 0.05 significntly different from qurtile 3 (undjusted) vlid confounders. A significntly higher distolic BP ws observed in qurtile four thn in qurtiles one nd three fter djusting for vlid confounders. LDL-C ws only lower in qurtile two thn in qurtile one before djustment while TC becme significntly higher in qurtiles two nd three thn in qurtile one fter djusting for vlid confounders. Tble VI compres CVD risk fctors mong TfR:ferritin rtio qurtiles. A significntly higher BMI ws observed in qurtiles two, three nd four thn in qurtile one. There were consistently lower vlues of WHR, TC, HDL-C, TG, LDL-C distolic BP, systolic BP nd CRP in the fourth qurtile thn in the first qurtile before djusting for vlid confounders. Only WC in qurtile two ws significntly higher thn in qurtile one fter djusting for vlid confounders Discussion This study exmined the ssocitions between iron sttus nd CVD risk fctors in blck South Africn women. Ferritin ws positively ssocited with TC (p < 0.05), HDL-C (p < 0.05), TG (p < 0.01), 183

6 LDL-C (p < 0.01), distolic nd systolic BP (p < 0.01), CRP (p < 0.01) nd lcohol consumption (p < 0.01). TfR:ferritin rtio ws negtively ssocited with the sme vribles s ferritin except for HDL-C. TfR ws negtively ssocited with TC, LDL-C nd lcohol consumption but positively ssocited with WHR. None of these ssocitions were retined fter djusting for ge, BMI, smoking, lcohol consumption nd CRP. WC nd WHR were significntly higher in the fourth qurtile of ferritin thn in the third qurtile fter djustment. In ddition, WC nd WHR in the third qurtile of ferritin were higher thn in the second qurtile fter djusting for vlid confounders. The hypothesis tht excess iron is cuslly linked to CVD dtes s fr bck s the 1980s, when Sullivn suggested tht incresed incidence of CVD in men nd postmenopusl women ws due to incresed body iron. 28 Free iron cn cuse the oxidtion of LDL-C, thereby mking it highly crdiotoxic. 29 Oxidised LDL-C hs the bility to cuse direct injury to endothelil cells, leding to genertion of fom cells. 29 However, the results of this study do not support this hypothesis (of n ssocition between excess iron nd CVD risk), becuse the observed ssocitions could be ttributed to the effects of other fctors such s ge, BMI, smoking, lcohol consumption nd infection on iron stores. Though very wek, WC, WHR, TC, TG, nd distolic BP were positively ssocited with ferritin when ge, BMI, smoking nd CRP only were djusted for in the nlysis. The inclusion of lcohol consumption on the list of vlid confounders removed this ssocition. This indictes tht lcohol consumption is strong predictor of iron sttus in this popultion, s confirmed by the study conducted by Gopne 30 in the sme popultion. Furthermore, this popultion seems to be t risk of iron deficiency, s indicted by men serum TfR concentrtion of 9.09 µg/ml (95% CI 8.77, 9.44), which could explin the lck of significnt ssocition between mesures of iron sttus nd the CVD risk fctors in the present study. Additionlly, 56% of the prticipnts hd men serum TfR concentrtion greter thn 8.50 µg/ml, indicting iron deficiency, s compred to 33% with incresed serum ferritin concentrtion (ferritin > 150 µg/l), indicting iron overlod. It is lso possible tht the ssocitions were not significnt becuse most of the women were not hypercholesterolemic (52% hd TC less thn or equl to 5 mmol/l). The findings of the present study do not gree with those of some studies tht hve exmined the reltionship between iron sttus nd CVD risk fctors. 6,31 These studies demonstrted positive ssocition between serum ferritin nd TC concentrtion. Postmenopusl women were used s prticipnts in these studies, which mkes their results less comprble to those of the present study, which ws composed of dult women both of pre- (76%) nd postmenopusl (24%) ge (over 55 yers). Menopuse itself hs been reported to result in incresed iron storge nd lipid production, owing to the bsence of the protective effect of endogenous oestrogen. 32 Additionlly, positive ssocition ws found between serum ferritin nd TG, but not TC, HDL-C nd BP, in helthy popultion of white Dnish women ged yers. 33 In the present study, TG ws positively ssocited with ferritin only before djusting for vlid confounders. It hs been proposed tht incresed serum TG my cuse n increse in the relese of smll LDL prticles through lipid trnsfer rection. 34 Smll LDL prticles re esily oxidised, the initil step in CVD development. 35 Increses in smll nd dense LDL prticles hve been linked to incresed CVD risk. 35 The findings of the present study re comprble to the observtions mde by Binkoski et l, who reported tht incresed body iron does not increse the susceptibility of LDL to oxidtive stress in women with low iron sttus. 36 A met-nlysis lso confirmed tht incresed iron stores do not ply significnt role in the development of CVD. 37 Additionlly, the Atherosclerotic Risk in Communities (ARIC) study 38 reported tht there ws no evidence of link between serum ferritin nd LDL oxidtion prmeters in either men or women in the USA (men ge 59 yers) without existing myocrdil infrction or history of ischemic hert ttck. In the Trnsition nd Helth during Urbnistion of South Africns (THUSA) study conducted 10 yers go in the sme popultion, Aderibigbe et l reported tht serum ferritin concentrtion ws significntly higher in the high WHR ctegory thn in the norml WHR ctegory. This observtion ws retined in women only fter djustment ws mde for ge, BMI nd smoking. 39 This is congruent with the findings of the present study, s WHR incresed significntly from the second to the fourth qurtile of ferritin. The sme trend ws observed for WC in the present study. This suggests tht centrl obesity contributes significntly to incresed serum ferritin concentrtion of women in this popultion. Ferritin, n cute-phse rectnt, is elevted during inflmmtion. 15 Obesity, now recognised s n inflmmtory condition, 40 my contribute to the elevted ferritin levels observed in this popultion. Hepcidin, the hormone tht inhibits the relese of iron from the stores nd reduces bsorption of iron, hs been shown to be elevted in obese individuls. 15 However, in the present study, obese women did not hve lower iron sttus. Adiposity, especilly centrlised dipose tissue, hs been reported to promote therogenetic rections by intercting with other CVD risk fctors. 14 Crist et l reported tht mrkers of lipid dmge such s oxidised low-density lipoprotein (oxldl) nd 15-isoprostne F 2α (PGF 2 ), nd not mrkers of DNA or protein dmge, contribute significntly to the development of CVD. 5 This supports the role of obesity in the pthogenesis of CVD. 41 A high WC hs been linked to incresed oxldl in both men nd women. 42 In this study, 31% of prticipnts exceeded the recommended limit for WC (< 88 cm), while 52% exceeded the reference limits for WHR (< 0.80). It hs been hypothesised tht iron overlod my not be problem in helthy popultion, but tht in popultion with obesity nd relted noncommunicble diseses, iron overlod my pose mjor thret. 14 No significnt correltion ws observed between serum ferritin nd TfR concentrtion fter djusting for vlid confounders. This implies tht one of these iron prmeters ws influenced by other fctors ffecting iron sttus; for exmple, ferritin is ffected by lcohol consumption nd inflmmtion. 43 In the present study, the men serum ferritin concentrtion in drinkers ( µg/l) ws double tht in non-drinkers ( µg/l). The men self-reported lcohol consumption in this popultion ws 7.74 g/d, which flls within the reference rnge for moderte drinking. 44 However, the men selfreported lcohol intke of women drinkers ws g/d, which is wy bove the reference rnge for moderte drinking

7 The mechnism by which lcohol increses serum ferritin concentrtion is not fully understood. 46 One of the speculted mechnisms is the lekge of intrcellulr ferritin by cell necrosis. 46 Serum ferritin, under norml circumstnces, is in equilibrium with intrcellulr ferritin. 24 Alcohol is thought to influence this equilibrium. 46 This is supported by the observtion tht serum ferritin in lcoholics correltes with incresed trnsminse levels, which were normlised when lcohol ws withdrwn. 47 Alcohol my lso hve direct effect on ferritin synthesis. 46 Alcohol induces ferritin synthesis in rt heptocyte primry cultures t low concentrtions, which cn esily be chieved in lcoholism. 46 It ws previously thought tht iron ccumultion hs to be severe to cuse oxidtive stress, but reserch findings suggest tht modertely excessive serum iron my contribute to formtion of oxygen rdicls, which cn initite oxidtion of LDL. 48 Oxidised LDL is scvenger receptor nd, when tken up by the mcrophges cn led to the formtion of fom cells, the most essentil cells of the ftty strek. 14 A men serum ferritin concentrtion of 80 µg/l hs been ssocited with significnt increses in incidence of hert disese for both genders. 28 In the present study, the men serum ferritin concentrtion ws µg/l. It is believed tht oxidtive stress itself cn relese the iron needed for production of rective species. Superoxide rdicls hve been observed to liberte iron from ferritin, thereby inducing lipid peroxidtion. It hs been proposed tht the role of iron in CVD involves the conversion of poorly rective free rdicls to highly rective ones. 29 Conclusion This popultion-bsed study suggests no significnt ssocition between iron sttus vribles nd CVD risk fctors except ferritin, which incresed with incresing bdominl obesity, s defined by WHR nd WC. This my pose greter risk for CVD s the proportion of iron-replete individuls increses. References 1. Hlliwell B, Gutteridge JMC. Role of free rdicls nd ctlytic metl ions in humn disese: n overview. In: Pcker L, Glzer AN, editors. Methods in enzymology. Sn Diego: Acdemic Press, 1990; p Rmkrishnn U, Kuklin E, Stein AD. Iron stores nd crdiovsculr disese risk fctors in women of reproductive ge in the United Sttes. 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