Environmental risk factors for multiple sclerosis. Part II: Noninfectious factors
Corresponding Author
Alberto Ascherio MD, DrPH
Department of Nutrition, Harvard School of Public Health, Boston, MA
Department of Epidemiology, Harvard School of Public Health, Boston, MA
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
Department of Nutrition and Epidemiology, Harvard School of Public Health, 665 Huntington Avenue, Building II, Room 335, Boston, MA 02115Search for more papers by this authorKassandra L. Munger MSc
Department of Nutrition, Harvard School of Public Health, Boston, MA
Search for more papers by this authorCorresponding Author
Alberto Ascherio MD, DrPH
Department of Nutrition, Harvard School of Public Health, Boston, MA
Department of Epidemiology, Harvard School of Public Health, Boston, MA
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
Department of Nutrition and Epidemiology, Harvard School of Public Health, 665 Huntington Avenue, Building II, Room 335, Boston, MA 02115Search for more papers by this authorKassandra L. Munger MSc
Department of Nutrition, Harvard School of Public Health, Boston, MA
Search for more papers by this authorAbstract
As discussed in Part I of this review, the geographic distribution of multiple sclerosis (MS) and the change in risk among migrants provide compelling evidence for the existence of strong environmental determinants of MS, where “environmental” is broadly defined to include differences in diet and other behaviors. As we did for infections, we focus here primarily on those factors that may contribute to explain the geographic variations in MS prevalence and the change in risk among migrants. Among these, sunlight exposure emerges as being the most likely candidate. Because the effects of sun exposure may be mediated by vitamin D, we also examine the evidence linking vitamin D intake or status to MS risk. Furthermore, we review the evidence on cigarette smoking, which cannot explain the geographic variations in MS risk, but may contribute to the recently reported increases in the female/male ratio in MS incidence. Other proposed risk factors for MS are mentioned only briefly; although we recognize that some of these might be genuine, evidence is usually sparse and unpersuasive. Ann Neurol 2007
References
- 1 Ascherio AM. Environmental risk factors for multiple sclerosis: the role of infection. Ann Neurol (in press)
- 2 Kurtzke JF, Beebe GW, Norman JE. Epidemiology of multiple sclerosis in US veterans: III. Migration and the risk of MS. Neurology 1985; 35: 672–678.
- 3 Miller DH, Hammond SR, McLeod JG, et al. Multiple sclerosis in Australia and New Zealand: are the determinants genetic or environmental? J Neurol Neurosurg Psychiatry 1990; 53: 903–905.
- 4 Acheson ED, Bachrach CA, Wright FM. Some comments on the relationship of the distribution of multiple sclerosis to latitude, solar radiation, and other variables. Acta Psychiatr Scand 1960; 147: 132–147.
10.1111/j.1600-0447.1960.tb08674.x Google Scholar
- 5 Sutherland JM, Tyrer JH, Eadie MJ. The prevalence of multiple sclerosis in Australia. Brain 1962; 85: 146–164.
- 6 van der Mei IA, Ponsonby AL, Blizzard L, Dwyer T. Regional variation in multiple sclerosis prevalence in Australia and its association with ambient ultraviolet radiation. Neuroepidemiology 2001; 20: 168–174.
- 7 Leibowitz U, Sharon D, Alter M. Geographical considerations in multiple sclerosis. Brain 1967; 90: 871–886.
- 8 Kurtzke JF. On the fine structure of the distribution of multiple sclerosis. Acta Neurol Scand 1967; 43: 257–282.
- 9 Freedman DM, Dosemeci M, Alavanja MC. Mortality from multiple sclerosis and exposure to residential and occupational solar radiation: a case-control study based on death certificates. Occup Environ Med 2000; 57: 418–421.
- 10 Goldacre MJ, Seagroatt V, Yeates D, Acheson ED. Skin cancer in people with multiple sclerosis: a record linkage study. J Epidemiol Community Health 2004; 58: 142–144.
- 11 Cendrowski W, Wender M, Dominik W, et al. Epidemiological study of multiple sclerosis in Western Poland. Eur Neurol 1969; 2: 90–108.
- 12 Antonovsky A, Leibowitz U, Smith HA, et al. Epidemiologic study of multiple sclerosis in Israel. Arch Neurol 1965; 13: 183–193.
- 13 van der Mei IAF, Ponsonby AL, Dwyer T, et al. Past exposure to sun, skin phenotype and risk of multiple sclerosis: a case-control study. BMJ 2003; 327: 316–321.
- 14 Islam KTS, Gauderman JW, Cozen W, Mack TM. Childhood sun-exposure modifies risk of multiple sclerosis among monozygotic twins [Abstract M-11]. Ann Neurol 2006; 60: S38 (Abstract).
- 15 Holick MF. Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. Am J Clin Nutr 2004; 80: 1678S–1688S.
- 16 Holick MF. The vitamin d epidemic and its health consequences. J Nutr 2005; 135: 2739S–2748S.
- 17 Moore CE, Murphy MM, Holick MF. Vitamin D intakes by children and adults in the United States differ among ethnic groups. J Nutr 2005; 135: 2478–2485.
- 18 Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988; 67: 373–378.
- 19 McKenna MJ, Freaney R, Byrne P, et al. Safety and efficacy of increasing wintertime vitamin D and calcium intake by milk fortification. QJM 1995; 88: 895–898.
- 20 Calvo MS, Whiting SJ. Prevalence of vitamin D insufficiency in Canada and the United States: importance to health status and efficacy of current food fortification and dietary supplement use. Nutr Rev 2003; 61: 107–113.
- 21 Rockell JE, Skeaff CM, Williams SM, Green TJ. Serum 25-hydroxyvitamin D concentrations of New Zealanders aged 15 years and older. Osteoporos Int 2006; 17: 1382–1389.
- 22 Valimaki VV, Loyttyniemi E, Valimaki MJ. Vitamin D fortification of milk products does not resolve hypovitaminosis D in young Finnish men. Eur J Clin Nutr (in press).
- 23 Bischoff-Ferrari HA, Giovannucci E, Willett WC, et al. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr 2006; 84: 18–28.
- 24 Goldberg P. Multiple sclerosis: vitamin D and calcium as environmental determinants of prevalence (a viewpoint). Part 1: sunlight, dietary factors and epidemiology. Int J Environ Stud 1974; 6: 19–27.
- 25 Swank RL, Lerstad O, Strøm A, Backer J. Multiple sclerosis in rural Norway. Its geographic and occupational incidence in relation to nutrition. N Engl J Med 1952; 246: 721–728.
- 26 Westlund K. Distribution and mortality time trend of multiple sclerosis and some other diseases in Norway. Acta Neurol Scand 1970; 46: 455–483.
- 27 Brustad M, Sandanger T, Aksnes L, Lund E. Vitamin D status in a rural population of northern Norway with high fish liver consumption. Public Health Nutr 2004; 7: 783–789.
- 28 Willett WC. Nutritional epidemiology. 2nd ed. New York: Oxford University Press, 1998: 514.
- 29 Munger KL, Zhang SM, O'Reilly E, et al. Vitamin D intake and incidence of multiple sclerosis. Neurology 2004; 62: 60–65.
- 30 Willett WC, Sampson L, Browne ML, et al. The use of a self-administered questionnaire to assess diet four years in the past. Am J Epidemiol 1988; 127: 188–199.
- 31 Salvini S, Hunter D, Sampson L, et al. Food-based validation of a dietary questionnaire: the effects of week-to-week variation in food consumption. Int J Epidemiol 1989; 18: 858–867.
- 32 Feskanich D, Willett WC, Colditz GA. Calcium, vitamin D, milk consumption, and hip fractures: a prospective study among postmenopausal women. Am J Clin Nutr 2003; 77: 504–511.
- 33 Holick MF. Resurrection of vitamin D deficiency and rickets. J Clin Invest 2006; 116: 2062–2072.
- 34 Munger KL, Levin LI, Hollis BW, et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA 2006; 296: 2832–2838.
- 35 Rubertone MV, Brundage JF. The Defense Medical Surveillance System and the Department of Defense serum repository: glimpses of the future of public health surveillance. Am J Public Health 2002; 92: 1900–1904.
- 36 Levin LI, Munger KL, Rubertone MV, et al. Temporal relationship between elevation of Epstein Barr virus antibody titers and initial onset of neurological symptoms in multiple sclerosis. JAMA 2005; 293: 2496–2500.
- 37 Lucas RM, Ponsonby AL. Considering the potential benefits as well as adverse effects of sun exposure: can all the potential benefits be provided by oral vitamin D supplementation? Prog Biophys Mol Biol 2006; 92: 140–149.
- 38 Hauser SL, Weiner HL, Che M, et al. Prevention of experimental allergic encephalomyelitis (EAE) in the SJL/J mouse by whole body ultraviolet irradiation. J Immunol 1984; 132: 1276–1281.
- 39 Aubin F. Mechanisms involved in ultraviolet light-induced immunosuppression. Eur J Dermatol 2003; 13: 515–523.
- 40 Hayes CE, Nashold FE, Spach KM, Pedersen LB. The immunological functions of the vitamin D endocrine system. Cell Mol Biol 2003; 49: 277–300.
- 41 Lemire JM, Archer DC. 1,25-dihydroxyvitamin D3 prevents the in vivo induction of murine experimental autoimmune encephalomyelitis. J Clin Invest 1991; 87: 1103–1107.
- 42 Cantorna MT, Hayes CE, DeLuca HF. 1,25-Dihydroxyvitamin D3 reversibly blocks the progression of relapsing encephalomyelitis, a model of multiple sclerosis. Proc Natl Acad Sci U S A 1996; 93: 7861–7864.
- 43 Spach KM, Hayes CE. Vitamin D3 confers protection from autoimmune encephalomyelitis only in female mice. J Immunol 2005; 175: 4119–4126.
- 44 Hayes CE, Cantorna MT, Deluca HF. Vitamin D and multiple sclerosis. Proc Soc Exp Biol Med 1997; 216: 21–27.
- 45 Meehan TF, DeLuca HF. The vitamin D receptor is necessary for 1alpha,25-dihydroxyvitamin D(3) to suppress experimental autoimmune encephalomyelitis in mice. Arch Biochem Biophys 2002; 408: 200–204.
- 46 Spach KM, Nashold FE, Dittel BN, Hayes CE. IL-10 signaling is essential for 1,25-dihydroxyvitamin d3-mediated inhibition of experimental autoimmune encephalomyelitis. J Immunol 2006; 177: 6030–6037.
- 47 Nashold FE, Hoag KA, Goverman J, Hayes CE. Rag-1-dependent cells are necessary for 1,25-dihydroxyvitamin D(3) prevention of experimental autoimmune encephalomyelitis. J Neuroimmunol 2001; 119: 16–29.
- 48 Hayes CE, Nashold FE, Spach KM, Pedersen LB. The immunological functions of the vitamin D endocrine system. Cell Mol Biol (Noisy-le-grand) 2003; 49: 277–300.
- 49 Zadshir A, Tareen N, Pan D, et al. The prevalence of hypovitaminosis D among US adults: data from the NHANES III. Ethn Dis 2005; 15: S5–97-101.
- 50 Looker AC, Dawson-Hughes B, Calvo MS, et al. Serum 25-hydroxyvitamin D status of adolescents and adults in two seasonal subpopulations from NHANES III. Bone 2002; 30: 771–777.
- 51 Hollis BW. Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D. J Nutr 2005; 135: 317–322.
- 52 Dawson-Hughes B, Heaney RP, Holick MF, et al. Estimates of optimal vitamin D status. Osteoporos Int 2005; 16: 713–716.
- 53 Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999; 69: 842–856.
- 54 Heaney RP, Davies KM, Chen TC, et al. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr 2003; 77: 204–210.
- 55 Nieves J, Cosman F, Herbert J, et al. High prevalence of vitamin D deficiency and reduced bone mass in multiple sclerosis. Neurology 1994; 44: 1687–1692.
- 56 Wingerchuk DM, Lesaux J, Rice GP, et al. A pilot study of oral calcitriol (1,25-dihydroxyvitamin D3) for relapsing-remitting multiple sclerosis. J Neurol Neurosurg Psychiatry 2005; 76: 1294–1296.
- 57 Auer DP, Schumann EM, Kumpfel T, et al. Seasonal fluctuations of gadolinium-enhancing magnetic resonance imaging lesions in multiple sclerosis. Ann Neurol 2000; 47: 276–277.
- 58 Embry AF, Snowdon LR, Vieth R. Vitamin D and seasonal fluctuations of gadolinium-enhancing magnetic resonance imaging lesions in multiple sclerosis. Ann Neurol 2000; 48: 271–272.
- 59 Rovaris M, Comi G, Sormani MP, et al. Effects of seasons on magnetic resonance imaging—measured disease activity in patients with multiple sclerosis. Ann Neurol 2001; 49: 415–416.
- 60 Tremlett H. Effects of seasons on magnetic resonance imaging-measured disease activity in patients with multiple sclerosis. Ann Neurol 2001; 50: 422–423.
- 61 Kurtzke JF, Heltberg A. Multiple sclerosis in the Faroe Islands: an epitome. J Clin Epidemiol 2001; 54: 1–22.
- 62 Franklin CR, Brickner RM. Vasospasm associated with multiple sclerosis. Arch Neruol Psychiatry 1947; 58: 125–162.
- 63 Spillane J. The effect of nicotine on spinocerebellar ataxia. Br Med J 1955; 2: 1345–1351.
- 64Anonymous. Smoking and multiple sclerosis. Br Med J 1964; 1: 773.
10.1136/bmj.1.5385.773-d Google Scholar
- 65 Perkin GD, Bowden P, Rose FC. Smoking and optic neuritis. Postgrad Med J 1975; 51: 382–385.
- 66 Perkin GD, Rose FC. Uhthoff's syndrome. Br J Ophthalmol 1976; 60: 60–63.
- 67 Emre M, de Decker C. Effects of cigarette smoking on motor functions in patients with multiple sclerosis. Arch Neurol 1992; 49: 1243–1247.
- 68 Emre M, de Decker C. Nicotine and CNS. Neurology 1987; 37: 1887–1888.
- 69 Ghadirian P, Dadgostar B, Azani R, Maisonneuve P. A case-control study of the association between socio-demographic, lifestyle and medical history factors and multiple sclerosis. Can J Public Health 2001; 92: 281–285.
- 70 Warren SA, Warren KG, Greenhill S, Paterson M. How multiple sclerosis is related to animal illness, stress and diabetes. CMAJ 1982; 126: 377–385.
- 71 Casetta I, Granieri E, Malagù S, et al. Environmental risk factors and multiple sclerosis: a community-based, case-control study in the province of Ferrara, Italy. Neuroepidemiology 1994; 13: 120–128.
- 72 Riise T, Nortvedt MW, Ascherio A. Smoking is a risk factor for multiple sclerosis. Neurology 2003; 61: 1122–1124.
- 73 Villard-Mackintosh L, Vessey MP. Oral contraceptives and reproductive factors in multiple sclerosis incidence. Contraception 1993; 47: 161–168.
- 74 Thorogood M, Hannaford PC. The influence of oral contraceptives on the risk of mulitple sclerosis. Br J Obstet Gynaecol 1998; 105: 1296–1299.
- 75 Hernàn MA, Olek MJ, Ascherio A. Cigarette smoking and incidence of multiple sclerosis. Am J Epidemiol 2001; 154: 69–74.
- 76 Hernan MA, Jick SS, Logroscino G, et al. Cigarette smoking and the progression of multiple sclerosis. Brain 2005; 128: 1461–1465.
- 77 Smith ADM, Duckett S, Waters AH. Neuropathological changes in chronic cyanide intoxication. Nature 1963; 200: 179–181.
- 78 The Cuba Neuropathy Field Investigation Team. Epidemic optic neuropathy in Cuba—clinical characterization and risk factors. The Cuba Neuropathy Field Investigation Team. N Engl J Med 1995; 333: 1176–1182.
- 79 Sopori ML, Kozak W. Immunomodulatory effects of cigarette smoke. J Neuroimmunol 1998; 83: 148–156.
- 80 Francus T, Klein RF, Staiano-Coico L, et al. Effects of tobacco glycoprotein (TGP) on the immune system. II. TGP stimulates the proliferation of human T cells and the differentiation of human B cells into Ig secreting cells. J Immunol 1988; 140: 1823–1829.
- 81 Costenbader KH, Karlson EW. Cigarette smoking and autoimmune disease: what can we learn from epidemiology? Lupus 2006; 15: 737–745.
- 82 Graham NM. The epidemiology of acute respiratory infections in children and adults: a global perspective. Epidemiol Rev 1990; 12: 149–178.
- 83 Orton SM, Herrera BM, Yee IM, et al. Sex ratio of multiple sclerosis in Canada: a longitudinal study. Lancet Neurol 2006; 5: 932–936.
- 84 Alter M, Yamoor M, Harshe M. Multiple sclerosis and nutrition. Arch Neurol 1974; 31: 267–272.
- 85 Agranoff BW, Goldberg D. Diet and the geographical distribution of multiple sclerosis. Lancet 1974; 2: 1061–1066.
- 86 Esparza ML, Sasaki S, Kesteloot H. Nutrition, latitude, and multiple sclerosis mortality: an ecologic study. Am J Epidemiol 1995; 142: 733–737.
- 87 Lauer K. The risk of multiple sclerosis in the U. S. A. in relation to sociogeographic features: a factor-analytic study. J Clin Epidemiol 1994; 47: 43–48.
- 88 Malosse D, Perron H, Sasco A, Seigneurin JM. Correlation between milk and dairy product consumption and multiple sclerosis prevalence: a worldwide study. Neuroepidemiology 1992; 11: 304–312.
- 89 Ghadirian P, Jain M, Ducic S, et al. Nutritional factors in the aetiology of multiple sclerosis: a case-control study in Montreal, Canada. Int J Epidemiol 1998; 27: 845–852.
- 90 Zhang SM, Willett WC, Hernan MA, et al. Dietary fat in relation to risk of multiple sclerosis among two large cohorts of women. Am J Epidemiol 2000; 152: 1056–1064.
- 91 Dworkin RH, Bates D, Millar JHD, Paty DW. Linoleic acid and multiple sclerosis: a reanalysis of three double-blind trials. Neurology 1984; 34: 1441–1445.
- 92 Bates D, Cartlidge NEF, French JM, et al. A double-blind controlled trial of long chain n-3 polyunsaturated fatty acids in the treatment of multiple sclerosis. J Neurol Neurosurg Psychiatry 1989; 52: 18–22.
- 93 Weinstock-Guttman B, Baier M, Park Y, et al. Low fat dietary intervention with omega-3 fatty acid supplementation in multiple sclerosis patients. Prostaglandins Leukot Essent Fatty Acids 2005; 73: 397–404.
- 94 Mickel HS. Multiple sclerosis: a new hypothesis. Perspect Biol Med 1975; 18: 363–374.
- 95 Ghadirian P, Jain M, Ducic S, et al. Nutritional factors in the aetiology of multiple sclerosis: a case-control study in Montreal, Canada. Int J Epidemiol 1998; 27: 845–852.
- 96 Berr C, Puel J, Clanet M, et al. Risk factors in multiple sclerosis: a population-based case-control study in Hautes-Pyrenees, France. Acta Neurol Scand 1989; 80: 46–50.
- 97 Zhang SM, Hernàn MA, Olek MJ, et al. Intakes of carotenoids, vitamin C, and vitamin E and MS risk among two large cohorts of women. Neurology 2001; 57: 75–80.
- 98 Whitacre CC, Reingold SC, O'Loony PA. A gender gap in autoimmunity. Science 1999; 283: 1277–1278.
- 99 Whitacre CC. Sex differences in autoimmune disease. Nat Immunol 2001; 2: 777–780.
- 100 Confavreux C, Hutchinson M, Hours MM, et al. Rate of pregnancy-related relapse in multiple sclerosis. Pregnancy in multiple sclerosis group. N Engl J Med 1998; 339: 285–291.
- 101 Alonso A, Jick SS, Olek MJ, et al. Recent use of oral contraceptives and the risk of multiple sclerosis. Arch Neurol 2005; 62: 1362–1365.
- 102 Hernàn MA, Hohol MJ, Olek MJ, et al. Oral contraceptives and the incidence of multiple sclerosis. Neurology 2000; 55: 848–854.
- 103 Marshall E. A shadow falls on hepatitis B vaccination effort. Science 1998; 281: 630–631.
- 104 Touze E, Fourrier A, Rue-Fenouche C, et al. Hepatitis B vaccination and first central nervous system demyelinating event: a case-control study. Neuroepidemiology 2002; 21: 180–186.
- 105 Zipp F, Weil JG, Einhaupl KM. No increase in demyelinating diseases after hepatitis B vaccination. Nat Med 1999; 5: 964–965.
- 106 Ascherio A, Zhang SM, Hernan MA, et al. Hepatitis B vaccination and the risk of multiple sclerosis. N Engl J Med 2001; 344: 327–332.
- 107 DeStefano F, Verstraeten T, Jackson LA, et al. Vaccinations and risk of central nervous system demyelinating diseases in adults. Arch Neurol 2003; 60: 504–509.
- 108 Sadovnick AD, Scheifele DW. School-based hepatitis B vaccination programme and adolescent multiple sclerosis. Lancet 2000; 355: 549–550.
- 109 Confavreux C, Suissa S, Saddier P, et al. Vaccinations and the risk of relapse in multiple sclerosis. Vaccines in Multiple Sclerosis Study Group. N Engl J Med 2001; 344: 319–326.
- 110 Hernan MA, Jick SS, Olek MJ, Jick H. Recombinant hepatitis B vaccine and the risk of multiple sclerosis: a prospective study. Neurology 2004; 63: 838–842.
- 111 Landtblom AM, Flodin U, Soderfeldt B, et al. Organic solvents and multiple sclerosis: a synthesis of the current evidence. Epidemiology 1996; 7: 429–433.
- 112 Landtblom AM. Exposure to organic solvents and multiple sclerosis. Neurology 1997; 49: S70–S74.
- 113 Mortensen JT, Bronnum-Hansen H, Rasmussen K. Multiple sclerosis and organic solvents. Epidemiology 1998; 9: 168–171.
- 114 Riise T, Moen BE, Kyvik KR. Organic solvents and the risk of multiple sclerosis. Epidemiology 2002; 13: 718–720.
- 115 Landtblom AM, Tondel M, Hjalmarsson P, et al. The risk for multiple sclerosis in female nurse anaesthetists: a register based study. Occup Environ Med 2006; 63: 387–389.
- 116 Goodin DS, Ebers GC, Johnson KP, et al. The relationship of MS to physical trauma and psychological stress: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology 1999; 52: 1737–1745.
- 117 Li J, Johansen C, Bronnum-Hansen H, et al. The risk of multiple sclerosis in bereaved parents: a nationwide cohort study in Denmark. Neurology 2004; 62: 726–729.
- 118 Hernan MA, Alonso A, Hernandez-Diaz S. Tetanus vaccination and risk of multiple sclerosis: a systematic review. Neurology 2006; 67: 212–215.
- 119 Alonso A, Jick SS, Jick H, Hernan MA. Antibiotic use and risk of multiple sclerosis. Am J Epidemiol 2006; 163: 997–1002.
- 120 Alonso A, Jick SS, Hernan MA. Allergy, histamine 1 receptor blockers, and the risk of multiple sclerosis. Neurology 2006; 66: 572–575.
- 121 Drulovic J, Dujmovic I, Stojsavljevic N, et al. Uric acid levels in sera from patients with multiple sclerosis. J Neurol 2001; 248: 121–126.
- 122 Rentzos M, Nikolaou C, Anagnostouli M, et al. Serum uric acid and multiple sclerosis. Clin Neurol Neurosurg 2006; 108: 527–531.