Taking your daily dose: Nutrition and Neural Tube Defects

SPINA bifida and anencephaly belong to a group of disorders known collectively as Neural Tube Defects (NTDs).

As their name suggests, they’re caused by a failure of the foetal neural tube to close in early pregnancy, meaning that the structures which later become the child’s spinal column and skull fail to develop properly.

Spina bifida shows a spectrum of disease severity ranging from mild paralysis of the lower limbs, right through to full paralysis of all four limbs with associated bladder and bowel dysfunction. However, anencephaly, which prevents the development of structures which later house the brain, is considered a fatal condition, with most of these infants surviving less than 24 hours.

Even though these disorders affect more than one in 1,000 live births in Ireland, we continue to have NTD rates that are higher than in other countries.

There’s evidence that Ireland’s high NTD rates may be at least partially attributable to our genes — those of Celtic ethnicity appear to have greater susceptibility irrespective of where they live in the world. However, there’s also much evidence that these high rates may relate to our diet and other health behaviours.

Research at the UCD Centre for Human Reproduction located at the Coombe Hospital in Dublin is now aiming to identify the factors which contribute to NTDs in Ireland, and to articulate the best ways to address these issues nationally. However, to understand the options available to us, it’s important to understand how these disorders occur.

About 70-75% of NTDs can be prevented if women supplemented with 400 micrograms of folic acid in the early stages of pregnancy. Yet, even though many young women are now aware of the importance of folic acid supplementation during pregnancy, it seems few are aware they should be taking this 400 microgram supplement if they are sexually active.

It is estimated that just 2% of 18-35-year-old Irish women, and only 1% of 36-50-year-old Irish women take a daily folic acid supplement. This is critically important, as the neural tube closes early in pregnancy — usually between day 21 and 23 post-conception. With less sthan 60% of Irish pregnancies being ‘planned’ this implies that in the other 40% of cases, there’s a high probability the woman will not be aware she’s pregnant before this critical developmental milestone occurs.

So, if you’re not taking a folic acid supplement regularly, and if you believe it’ll be time enough to get started once you know you’re pregnant, there’s a strong likelihood that you’ll have missed the boat.

The next question that arises is whether the advice to supplement with folic acid is ever likely to address this problem effectively. For example, we know that wealthier, educated women are more likely to follow this guidance than poorer, less well-educated women. Therefore, even if the supplementation message does finally begin to get through, more socially vulnerable women may not heed this advice to the same extent as their more advantaged peers. This is an important consideration as poorer women consume less folate in their diet, making them the main priority target group for increased intake.

The most realistic option may be to introduce compulsory fortification of a staple foodstuff like wheatflour, as the US and Canada have done since 1998.

However, even with this strategy, several obstacles remain to be overcome. For example, how do we avoid overdosing people who have a high intake of the chosen staple food? How do we assuage the concerns of people who argue that their civil liberties are being infringed by this imposed alteration of the food chain?

One thing is clear, however. The human, social and economic costs of these cruel, debilitating disorders are too great for us not to act now, to develop more effective interventions in this area.

* Dr Daniel McCartney is a lecturer in human nutrition and dietetics at DIT