# Presentation: 153404

## What is the Minimum Effective Dose of Folic Acid for Preventing NTDs?

- James L. Mills, M.D., M.S.
- Caroline Signore, M.D.
- NICHD

## Minimum Effective Dose:Outline

- Why is this a difficult question to answer?
- How can we estimate how much folic acid is needed?
- Actual experience with fortification
- Conclusions

## Minimum Effective Dose:Why is This a Difficult Question to Answer?

## The Definitive Study

- Test reduced doses until NTD rates rise
- 400 μg	  Protective
- 300 μg    Protective
- 200 μg    Protective
- 100 μg    Not Protective

**UNETHICAL**

## What do we Know About Effective Dose?

- Clinical trial doses—definitely work, but too high
- 	MRC, 1991:		4 mg
- 	Czeizel, 1992:	800 μg
- Case control study doses—presumed to work, but are lower doses effective?
- 	Most U.S. studies reported on 400 μg

## Complication: Genetic Differences in Folate Metabolism

| MTHFR Genotype | Mean RCF (μg/L) |
| --- | --- |
| CC | 347 |
| CT | 314 |
| TT | 284* |

- Molloy AM, et al., *Lancet*, 1997; **p*<0.01

## How Can We Estimate How Much Folic Acid is Needed?

## Maternal Red Cell Folate vs. NTD Risk in Dublin

- Study Design
- Reviewed early pregnancy maternal RCF from nested case-control study of 84 cases NTD and 266 normal controls
- Logistic regression analysis to examine relationship between RCF and NTD risk

- Daly L, et al., *JAMA, *1995

##  Maternal RCF vs. NTD Risk in Dublin

- Continuous dose-response relationship
- RCF < 150 ng/mL Risk  6.6/1000
- RCF > 400 ng/mL Risk  0.8/1000

- Daly L, et al., *JAMA*, 1995

##  Maternal RCF vs. NTD Risk in Dublin

- Curve continues down
- Risk  0.2/1000?

- Daly L, et al., *JAMA*, 1995

##  Maternal RCF vs. NTD Risk in Dublin

- Curve flattens out (genetic Mendelian defects)
- Risk  0.5/1000?
- Unable to confirm optimal RCF level, but 400 ng/mL is highly protective

- Daly L, et al., *JAMA*, 1995

## How Much Folic Acid is Needed to Raise RCF to Protective Levels?

## NICHD/Trinity College/Health Research Board Trial

- Study design
- Randomized, placebo-controlled trial
- 121 patients randomized to receive placebo, 100 μg, 200 μg, or 400 μg folic acid/d
- Compliance assessed by sign-in sheets over 6 mo. study period

- Daly S, et al., *Lancet*, 1997

## Results

| Group | N | Initial Median RCF μg/L | Final Median RCF μg/L | Median Change μg/L |
| --- | --- | --- | --- | --- |
| Placebo | 19 | 335 | 311 | -12 |
| 100 μg/d | 22 | 309 | 375* | 67 |
| 200 μg/d | 28 | 311 | 475* | 130 |
| 400 μg/d | 26 | 350 | 571* | 200 |

- Daly S, et al. *Lancet*, 1997

- * p < 0.001

## RCF and NTD Risk Calculation

- Initial and post-treatment RCF values substituted into regression equation from L. Daly, et al. to derive estimated change in NTD risk

- Daly S, et al. *Lancet*, 1997

## Results

| Treatment
Group | N | Estimated Reduction in NTD Risk |
| --- | --- | --- |
| Placebo | 19 | 0 |
| 100 μg/d | 22 | 22% |
| 200 μg/d | 28 | 41% |
| 400 μg/d | 26 | 47% |

- Daly S, et al. *Lancet*, 1997

## Minimum estimate
(considering non-compliance):

~200 μg/d will 
decrease NTD rate by 41%

- (considering non-compliance):
**~200 μg/d will **
**decrease NTD rate by 41%**

## Literature Review and Calculation of Folic Acid Effect on Serum Folate

- Mathematical model based on trials of folic acid supplementation on plasma folate
- Calculated a dose-response equation

- Wald N, et al.  *Lancet,* 2001.

## Quantifying the Effect of Folic Acid

- Wald N, et al.  *Lancet,* 2001.

## Predicted plasma folate levels were far lower than actual levels in NHANES 1999-2000

The effects were inconsistent
	by age

- The effects were inconsistent
- 	by age

## Explanations

- Non-compliance would lead to an underestimation of effect
- Studies selected for the model had insufficient duration of exposure to reach stable serum folate levels, resulting in an underestimation of effect

## Exposure Time Required to Reach Stable Folate Levels

- Larger doses of folic acid require a longer period to achieve steady serum or plasma concentration

- Quinlivan EP and Gregory JF, *Am J Clin Nutr, *2003

## Was Duration of Exposure Sufficient to Produce Stable Levels?

|  | Adequate
Duration | Inadequate Duration |
| --- | --- | --- |
| Mean Age
20-35 | 2 (33%) | 4 (67%) |
| Mean Age
40-65 | 4 (50%) | 4 (50%) |
| TOTAL | 6 (43%) | 8 (57%) |

## Differences May be Due to Inadequate Time for Stabilization

- Wald N, et al.  *Lancet,* 2001.

## Studies used in Wald’s model led to an underestimation of folic acid effect on serum folate

## What Are Current Exposure Levels?

## Estimating DailyFolic Acid Intake After Fortification

## How Has Fortification Affected Folate Levels?

## Serum Folate Levels Pre- and Post-Fortification

**4.6**

**4.8**

**12.6**

**5.4**

**8.2**

**6.1**

****** ****171%**

****** ****48%**

****** ****117%**

**13.0**

**18.7**

**10.0**

## RCF Levels Pre- and Post-Fortification

****** ****65%**

****** ****40%**

**104**

**94**

**160**

**233**

**264**

**327**

## Summary

- Fortification probably increases folic acid exposure by 200 μg/day or more
- Serum and red cell folate levels have risen dramatically (by 171% and 65%, respectively)

## Actual Experience with Fortification

## The Gold Standard

- How much has the additional
- 200 μg/day decreased NTD rates?

## Estimates Vary Because of Ascertainment Problems

- Stevenson RE, et al., *Pediatrics*, 2000

| Method of Detection | Percent |
| --- | --- |
| Ultrasonography | 55% |
| MSAFP | 25% |
| AF AFP | 3% |
| Delivery | 17% |

## Experience:  Nova Scotia

- Population based study of all NTDs from live births, stillbirths, and terminations
- Compared pre- and post-fortification at 150 μg/100 g
- Total NTD incidence fell by 54%
- 2.58/1000  1.17/1000

- Persad VL, et al., *CMAJ, 2002*

## Estimated Effect

- Canada:  fortification at 150 μg /100 g grain   50% reduction
- U.S. data with comparably ascertained cases are still not widely available

## Conclusions

## Conclusions

- It is difficult to pinpoint the lowest effective dose of folic acid
- Data from Ireland indicate 200 μg/day will prevent at least 40% of NTDs

## Conclusions

- Actual experience in Canada indicates estimated doses of 200+ μg/day will prevent 50% or more
- In the U.S., ~50% prevention may be the maximum, or ~70% prevention may be possible—have we “maxed out?”

## Conclusions

- Given food fortification and supplement use in the U.S., many women will not need fortified OCs
- For women using supplements, fortified OCs might put them over the IOM’s recommended limit
- For other women, who do not take supplements and who eat less fortified food, fortified OCs could be beneficial