Official Statistics

National Diet and Nutrition Survey: republished supplementary report on blood folate results

Updated 28 November 2017

Update on forthcoming revisions to the report

We will publish a revised version of ‘National Diet and Nutrition Survey (NDNS) rolling programme: supplementary report, blood folate results for the UK as a whole, Scotland, Northern Ireland (Years 1 to 4 combined) and Wales (Years 2 to 5 combined)’ on 28 November 2017. It was originally published in March 2015.

This notice updates users on the changes to be made to the report.

Changes

The widely accepted Institute of Medicine thresholds^{[footnote 1]} for indicating risk of clinical deficiency of folate as shown by haematological change, are used in the revised report, giving estimates of the UK population at risk of clinical folate deficiency, for example anaemia.

The thresholds agreed by the World Health Organization (WHO) in 2008 to define biochemical folate deficiency^{[footnote 2]} are no longer used in the report. This is because the laboratory assays for blood folate on which they are based are different from the blood folate assays used in NDNS rolling programme. New assay-adjusted thresholds have since been published^{[footnote 3]} but there is uncertainty about their applicability to the UK population. They have not been used in the report. Instead, estimated threshold ranges are used, derived from statistical modelling of the NDNS data, to give an indication of the proportion of population age and sex groups which might be at risk of biochemical insufficiency. The new estimated threshold ranges are higher than the WHO thresholds used in the original report so the estimated percentages of age and sex groups at risk of biochemical insufficiency will increase.

Blood folate levels for women of childbearing age are considered in relation to the assay-adjusted WHO thresholds for increased risk of fetal folate-sensitive neural tube defects (NTDs) published in 2015^{[footnote 4]}.

Results have been updated to correct for a calibration issue that led to a bias in the assay for unmetabolised (free) folic acid which was identified by the laboratory after publication of the original report. This correction reduces median folic acid concentrations by 25 to 30%, median serum total folate concentrations by around 0.5% and has a negligible impact on red blood cell folate. Overall, the impact on published results is very small. Further details can be found in the correction notice published in October 2016.

Footnotes

1. Institute of Medicine (1998) Dietary Reference Intakes for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin and choline. Washington, DC: The National Academies Press. https://doi.org/10.17226/6015. ↩

2. WHO. Conclusions of a WHO technical consultation on folate and vitamin B12 deficiencies. Food and Nutrition Bulletin. 2008: 29. S238-S244 ↩

3. Pfeiffer CM, Sternberg MR, Hamner HC, Crider KS, Lacher DA, Rogers IM, Bailey RL, Yetley EA (2016) Applying inappropriate cutoffs leading to misinterpretation of folate status in the US population. Am. J Clin Nutr. Doi: 10.3945/ajcn.116.138529 ↩

4. Tinker SC, Hamner H, Qi YP, Crider KS. U.S. Women of Childbearing Age Who Are at Possible Increased Risk of a Neural Tube Defect-Affected Pregnancy Due to Suboptimal Red Blood Cell Folate Concentrations, National Health and Nutrition Examination Survey, 2007–2010. National Health and Nutrition Examination Survey 2007 to 2012. Birth Defects Research (Part A) 103:517–526, 2015. ↩