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Low folate status and indoor pollution are risk factors for endemic optic neuropathy in Tanzania
  1. Katherine E Hodson1,
  2. Richard J Bowman2,
  3. Milka Mafwiri3,
  4. Mark Wood4,
  5. Vincent Mhoro4,
  6. Sharon E Cox5
  1. 1Department of Nutrition & Public Health Intervention Research, London School of Hygiene & Tropical Medicine, London, UK
  2. 2International Centre for Eye Health, London School of Hygiene & Tropical Medicine, London, UK
  3. 3Department of Ophthalmology, Muhimbili University of health & Allied Sciences, Dar-es-Salaam, Tanzania
  4. 4Department of Ophthalmology, CCBRT, Dar-es-Salaam, Tanzania
  5. 5MRC International Nutrition Group, London School of Hygiene & Tropical Medicine, London, UK
  1. Correspondence to Dr Richard Bowman, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK; richard.bowman{at}LSHTM.AC.UK


Aims Bilateral optic neuropathy in Dar-es-Salaam, Tanzania was first reported as an epidemic in 1988. Now argued to be endemic in 2010, the aetiology remains unclear. The authors investigated the hypothesis that low folate and vitamin B12 status are associated with optic neuropathy, and also sought to investigate whether mercury, commonly used drugs, dietary factors and indoor pollution may also be risk factors.

Methods 57 cases and 102 controls were recruited from two tertiary referral centres in Dar-es-Salaam. Data were collected on demographic characteristics, diet, medication history and HIV status. Folate and vitamin B12 (holo-transcobalamin) were measured in stored serum samples. Exposure to mercury was assessed from concentrations in random urine samples.

Results Cooking indoors more than twice per week (OR 54.48 (95% CI 9.30 to 319.10)) and indoor use of charcoal or firewood (OR 21.20 (95% CI 2.51 to 179.36)) increased the risk of optic neuropathy. Risk was reduced in those with a higher folate status (highest versus lowest quartile OR=0.11 (95% CI 0.02 to 0.51)) and higher protein intakes (OR=0.84 (95% CI 0.72 to 0.96). No association was found with mercury exposure or any common drug or food commodity.

Conclusion This study presents the first direct evidence of low folate status and indoor pollution in the aetiology of endemic bilateral optic neuropathy in Tanzania.

  • Optic
  • neuropathy
  • folate
  • oxidative stress
  • optic nerve
  • public health

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  • Funding This study was funded by a Chadwick Foundation Travel Scholarship, UCL, UK; a Nestlé Travel Scholarship, LSHTM, UK & Lootah BC Gas, Dubai.

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval Approval was granted by the Research Ethics Committee London School of Hygiene & Tropical Medicine (Application no: 08/156) and Muhimbili University of Health and Allied Sciences, Dar-es-Salaam, Tanzania (Ref: MU/RP/AEC/Vol.XIII/61).

  • Provenance and peer review Not commissioned; externally peer reviewed.