Skip to main content
    • Aa
    • Aa

Folate and vitamin B12

  • John M. Scott (a1)

The folates are made up of a pterdine ring attached to a p-aminobenzoate and a polyglutamyl chain. The active form is tetrahydrofolate which can have C1 units enzymically attached. These C1 units (as a formyl group) are passed on to enzymes in the purine pathway that insert the C−2 and C−8 into the purine ring. A methylene group (−CH2−) attached to tetrahydrofolate is used to convert the uracil-type pyrimidine base found in RNA into the thymine base found in DNA. A further folate cofactor, i.e. 5-methyltetrahydrofolate, is involved in the remethylation of the homocysteine produced in the methylation cycle back to methionine. After activation to S-adenosylmethionine this acts as a methyl donor for the dozens of different methyltransferases present in all cells. Folate deficiency results in reduction of purine and pyrimidine biosynthesis and consequently DNA biosynthesis and cell division. This process is most easily seen in a reduction of erythrocytes causing anaemia. Reduction in the methylation cycle has multiple effects less easy to identify. One such effect is certainly on the nerve cells, because interruption of the methylation cycle causing neuropathy can also happen in vitamin B12 deficiency due to reduced activity of the vitamin B12-dependent enzyme methionine synthase (EC In vitamin B12 deficiency, blocking of the methylation cycle causes the folate cofactors in the cell to become trapped as 5-methyltetrahydrofolate. This process in turn produces a pseudo folate deficiency in such cells, preventing cell division and giving rise to an anaemia identical to that seen in folate deficiency.

    • Send article to Kindle

      To send this article to your Kindle, first ensure is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle.

      Note you can select to send to either the or variations. ‘’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

      Find out more about the Kindle Personal Document Service.

      Folate and vitamin B12
      Available formats
      Send article to Dropbox

      To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about sending content to Dropbox.

      Folate and vitamin B12
      Available formats
      Send article to Google Drive

      To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about sending content to Google Drive.

      Folate and vitamin B12
      Available formats
Corresponding author
Corresponding author: Professor John M. Scott, fax +353 1677 2400, email
Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

R Carmel (1995) Malabsorption of food cobalamin. In Bailliere's Clinical Haematology, vol. 8, pp. 639655 [ SM Wickramsinghe , editor]. London:Bailliere Tindall.

AE Czeizel (1996) Reduction in urinary tract and cardiovascular defects by periconceptional multivitamin supplementation. American Journal of Medical Genetics 62, 179183.

LE Daly , PM Kirke , A Molloy , DG Weir & JM Scott (1995) Folate levels and neural tube defects. Implications for prevention. Journal of the American Medical Association 274, 16981702.

J Lindenbaum , DG Savage , SP Stabler & RH Allen (1990) Diagnosis of cobalamin deficiency: II. Relative sensitivities of serum cobalamin, methylmalonic acid, and total homocysteine concentrations. American Journal of Hematology 34, 99107.

J McPartlin , A Halligan , JM Scott , M Darling & DG Weir (1993) Accelerated folate breakdown in pregnancy. Lancet 341, 148149.

M Manzoor & J Runcie (1976) Folate-responsive neuropathy: report of 10 cases. British Medical Journal 1, 11761178.

JL Mills , P McPartlin , PM Kirke , YJ Lee , MR Conley , DG Weir & JM Scott (1995) Homocysteine metabolism in pregnancies complicated by neural tube defects. Lancet 345, 149151.

AM Molloy , S Daly , JL Mills , PN Kirke , AS Whitehead , D Ramsbottom , M Conley , DG Weir & JM Scott (1997) Thermolabile variant of 5,10-methylenetetrahydrofolate reductase associated with low red cell folates: Implications for folate intake recommendations. Lancet 349, 15911593.

JM Scott , P Kirke , AM Molloy , L Daly & D Weir (1994) The role of folate in the prevention of neural tube defects. Proceedings of the Nutrition Society 53, 631636.

JM Scott & DG Weir (1996) Homocysteine and cardiovascular disease. Quarterly Journal of Medicine 89, 561563.

M Tolarova & J Harris (1995) Reduced recurrence of orofacial clefts after periconceptional supplementation with high dose folic acid and multivitamins. Teratology 51, 7178.

NJ Wald , HC Watt , MR Law , DG Weir , J McPartlin & JM Scott (1998) Homocysteine and ischaemic heart disease: results of a prospective study with implications on prevention. Archives of Internal Medicine 158, 862867.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Proceedings of the Nutrition Society
  • ISSN: 0029-6651
  • EISSN: 1475-2719
  • URL: /core/journals/proceedings-of-the-nutrition-society
Please enter your name
Please enter a valid email address
Who would you like to send this to? *



Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 411 *
Loading metrics...

Abstract views

Total abstract views: 408 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 29th May 2017. This data will be updated every 24 hours.