Abstract
Two randomised controlled trials, published in the early 1990s, proved that periconceptional use of folic acid containing supplements reduces the risk of a neural tube defect (NTD)-affected pregnancy. In New Zealand in 2009, mandatory folic acid fortification of all bread was deferred until 2012. In the interim, the bread manufacturers agreed to add folic acid at 200 µg per 100 g bread to approximately 30% of their range.
The overall objective of this PhD thesis was to monitor the impact of this voluntary bread fortification programme on the folate status of women of childbearing age.
Knowledge of the possible adverse effects of folic acid is needed to make an informed judgement on the best fortification strategy. The first specific aim of this thesis was to review the epidemiological studies relating folate intakes, folate status or folate supplementation to all cancer or colorectal cancer. An updated meta-analysis of the effect of folate supplements on all cancer showed no significant effect [RR: 1.06 (95% CI: 0.99 to 1.13).
The second specific aim was to determine the baseline blood folate status of women of childbearing age prior to the introduction of the voluntary bread fortification programme. Of the female participants of childbearing age (n = 663) from the 2008/09 New Zealand Adult Nutrition Survey, the geometric mean serum and erythrocyte folate concentrations were 23 nmol/L, and 720 nmol/L, respectively.
The third specific aim was to determine the folic acid content of fortified breads available for sale in New Zealand. The top ranked fortified breads (by sales volume) were tested (n = 17). Five contained less than 50 µg folic acid per 100 g of bread, ten contained between 100 to 300 µg, and two contained between 400 to 500 µg.
The fourth specific aim was to determine the time to reach steady state erythrocyte folate concentrations following a sustained increase in additional folate intake. Data from a two-year randomised daily folate supplementation placebo-controlled trial (n = 258) indicated that erythrocyte folate concentrations reached a new steady state within 12 months.
The fifth specific aim was to determine the consumption of folic acid fortified foods, and the blood folate status of women of childbearing age following the introduction of the voluntary bread fortification programme. For this purpose, the 2011 Folate and Women’s Health Survey (n = 288) was conducted. The geometric mean serum and erythrocyte folate concentrations were 30 nmol/L and 996 nmol/L, respectively. Compared to those who did not consume fortified bread, consumers had 25% significantly higher serum folate concentrations.
The voluntary bread fortification programme has coincided with an increase in the folate status of women of childbearing age. The difference in blood folate status between the two surveys is larger than what would be expected from the voluntary bread folic acid fortification programme alone, given that just 18% of the participants in the latter survey reported consuming fortified bread in the past week. There was also a concurrent increase in the number of folic acid fortified breakfast cereals on the market.