Folic acid supplementation
49
Health Reports, Volume 15, No. 3, May 2004 Statistics Canada, Catalogue 82-003
In 1999, the rate of open neural tube defects, the
two most common of which are spina bifida and
anencephaly, was 5.6 for every 10,000 births.
1
These
defects occur in the first four weeks of pregnancy,
usually before most women know they are pregnant.
2
The prevalence of open neural tube defects tends
to be lower among children of women who have
taken folic acid supplements around the time of
conception.
3-5
Folic acid is a B-vitamin that facilitates nucleic
acid synthesis, which is
necessary for normal cell
replication. Naturally
occurring folates are found
in broccoli, spinach, Brussels
sprouts, corn, legumes, and
oranges.
If women relied only on
dietary intake, a substantial
proportion of the
childbearing population
would receive a lower level
of folic acid than is
recommended for
preventing neural tube
defects.
6
A diet that
conforms to Canada’s Food
Guide for Healthy Eating
would provide about 0.2
milligrams of folic acid a day.
The Society of Obstetricians
and Gynaecologists of Canada recommends that
women who could become pregnant should take a
multivitamin containing 0.4 to 1.0 milligrams of folic
acid every day, in addition to the amount that would
be found in a healthy diet.
7
Health Canada advises
that daily folic acid supplementation be started at
least two to three months before conception and
continued throughout the first trimester.
8
FOLIC ACID SUPPLEMENTATIONFOLIC ACID SUPPLEMENTATION
FOLIC ACID SUPPLEMENTATIONFOLIC ACID SUPPLEMENTATION
FOLIC ACID SUPPLEMENTATION by Wayne J. Millar
Less than halfLess than half
Less than halfLess than half
Less than half
In 2000/01, as part of the Canadian Community
Health Survey, women aged 15 to 55 who had given
birth in the previous five years were asked questions
about their pregnancy, including, “Did you take a
vitamin supplement containing folic acid before your
(last) pregnancy, that is, before you found out that
you were pregnant?” Of the estimated 1.5 million
women in this age range who had given birth, 45%
reported that they had used
vitamin supplements
containing folic acid before
their last pregnancy.
The older the mother, the
more likely she was to have
used folic acid supplements.
The figure ranged from 33%
among women aged 15 to 24
to 48% at age 30 or older.
Although unplanned
pregnancies occur in all
marital status groups,
pregnancies among married
women are more likely to be
planned, and therefore, may
be more likely to involve the
use of folic acid supplements
before conception.
9
Close to
half (48%) of women who
were married had taken folic
acid supplements, compared
with 31% who were not married.
Folic acid supplementation was associated with
several socio-economic factors. Use tended to be
higher among urban than rural mothers, and among
those in higher-income households. Level of
education was also associated with use, which was
lowest among women with less than high school
*
34
39
48
56
Low Lower-middle Upper-middle High
Household income
*
*
*
Canada (45%)
*
Percentage of women aged 15 to 55 who took folic acid
supplements before pregnancy, by household income
Data source: 2000/01 Canadian Community Health Survey
* Significantly different from rate for Canada (p < 0.05)
Folic acid supplementation50
Health Reports, Volume 15, No. 3, May 2004 Statistics Canada, Catalogue 82-003
Use of folic acid supplements beforeUse of folic acid supplements before
Use of folic acid supplements beforeUse of folic acid supplements before
Use of folic acid supplements before
pregnancy among women who gave birthpregnancy among women who gave birth
pregnancy among women who gave birthpregnancy among women who gave birth
pregnancy among women who gave birth
in previous five years, 2000/01in previous five years, 2000/01
in previous five years, 2000/01in previous five years, 2000/01
in previous five years, 2000/01
Estimated Took folic acid
population
’000 ’000 %
Total 1,525 690 45
Age
15-24 191 63 33*
25-29 375 163 43
30-55 960 465 48*
Marital status
Married 1,296 620 48*
Not married 229 70 31*
Missing F F F
Province/Territory
Newfoundland 25 11 44
Prince Edward Island 7 3 43
Nova Scotia 43 22 50
New Brunswick 35 16 45
Québec 346 105 30*
Ontario 607 311 51*
Manitoba 55 25 46
Saskatchewan 51 22 43
Alberta 163 81 49*
British Columbia 184 91 49*
Yukon Territory 2 1 42
Northwest Territories 3 1 31*
Nunavut 3 1 41
Rural/Urban
Rural 271 110 41*
Urban 1,254 580 46*
Household Income
Low 229 78 34*
Lower-middle 367 145 39*
Upper-middle 505 242 48*
High 337 187 56*
Missing 88 38 43
Education
Less than high school graduation 202 67 33*
High school graduation 313 132 42*
Some postsecondary 138 49 35*
College/University graduation 860 439 51*
Missing F F F
Immigrant status
Immigrant 357 150 42
Non-immigrant 1,162 539 46*
Missing F F F
Data source: 2000/01 Canadian Community Health Survey
* Significantly different from value for Canada (p < 0.05)
F Coefficient of variation greater than 33.3%
graduation, and highest among postsecondary
graduates. The percentage of immigrant mothers
who had used folic acid supplements was lower than
the figure for those who were Canadian-born: 42%
versus 46%.
Declining rates of neural tubeDeclining rates of neural tube
Declining rates of neural tubeDeclining rates of neural tube
Declining rates of neural tube
defectsdefects
defectsdefects
defects
The 1999 level of open neural tube defects in
Canada—5.6 per 10,000 births—was substantially
lower than the rate of 11.1 per 10,000 in 1989.
1
Factors other than taking folic acid supplements
probably contributed to this decline. Food
fortification with folic acid is not likely involved, as
it was not mandated in Canada until 1998. However,
prenatal screening to detect congenital anomalies
may have resulted in some women opting for
therapeutic abortion.
10
For instance, in England and
Wales, the incidence of neural tube defects fell from
3.2 per 1,000 births in the early 1970s to 0.1 per
1,000 births in 1997. About 40% of this decline
was attributed to prenatal screening and termination
of pregnancy, with the remainder accounted for by
a decline in incidence, that coincided with an increase
in dietary folate.
11
Rate of neural tube defects, Canada, 1989 to 1999
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
0
2
4
6
8
10
12
Per 10,000 total births
†
Data source: Health Canada, Canadian Congenital Anomalies Surveillance System
Note: Excludes Nova Scotia
† Live births and stillbirths
Folic acid supplementation
51
Health Reports, Volume 15, No. 3, May 2004 Statistics Canada, Catalogue 82-003
Wayne J. Millar (613-951-1631; [email protected]) is
with the Health Statistics Division at Statistics Canada, Ottawa,
Ontario, K1A 0T6
References
3 Milunsky A, Jick H, Jick SS, et al. Multivitamin/folic acid
supplementation in early pregnancy reduces the prevalence
of neural tube defects. Journal of the American Medical
Association 1989; 262(20): 2847-52.
4 MIRC Vitamin Study Research Group. Prevention of neural
tube defects: results of the Medical Research Vitamin Council
Study. Lancet 1991; 338: 131-7.
5 Czeizel AE, Dudas I. Prevention of the first occurrence of
neural-tube defects by periconceptional vitamin
supplementation. New England Journal of Medicine 1992:
327(26): 1832-5.
1 Kohut R, Rusen ID, Lowrey RB, eds. Congenital Anomalies in
Canada - A Perinatal Health Report, 2002 (Catalogue H39-641/
2002E) Ottawa: Minister of Public Works and Government
Services Canada, 2002.
2 Elwood JM, Little J, Elwood JH. Epidemiology and Control of
Neural Tube Defects. Oxford: Oxford University Press, 1992.
Data sourceData source
Data sourceData source
Data source
Use of vitamin supplements containing folic acid before
pregnancy was estimated using data from the first cycle of the
Canadian Community Health Survey (CCHS), which was
conducted from September 2000 to October 2001.
12
The
survey covers the population aged 12 or older who were living
in private households at the time. It does not include residents
of Indian reserves, Canadian Forces Bases, or some remote
areas. The response rate for the first cycle was 85%; the total
sample size was 131,535.
All differences were tested to ensure statistical significance;
that is, they did not occur simply by chance. To account for
survey design effects, standard errors and coefficients of
variation were estimated using the bootstrap method.
13-15
A
significance level of p < 0.05 was applied in all cases.
The information about the use of folic acid supplements is
based on a sample of 7,875 women aged 15 to 55 who had
given birth in the previous five years, representing a population
of 1.5 million women. The survey did not ask the women if
they had planned their pregnancy or about their knowledge of
folic acid. No information is available about the dosage of
folic acid or the frequency of use. The percentage of women
taking folic acid may be underestimated, because some women
may not know that multivitamins contain it.
44
43
50
45
30
51
46
43
49 49
42
31
41
Nfld PEI NS NB Qué Ont Man Sask Alta BC Yukon NWT Nunavut
*
*
*
*
*
Canada (45%)
Percentage of women aged 15 to 55 who took folic acid
before pregnancy, by province/territory
Data source: 2000/01 Canadian Community Health Survey
* Significantly different from rate for Canada (p < 0.05)
Provincial and territorial rates of folic acid
supplementation varied from 30% in Québec and
31% in the Northwest Territories to 51% in Ontario.
Rates in Alberta and British Columbia were also
above the national level.
In Québec, where the reported use of folic acid
supplementation is low, the rate of neural tube
defects is relatively high.
7
However, in
Newfoundland, where the level of folic acid
supplementation matches the national figure, the rate
of neural tube defects is the same as in Québec.
7
Folic acid supplementation52
Health Reports, Volume 15, No. 3, May 2004 Statistics Canada, Catalogue 82-003
6 Werler MM, Louik C, Mitchell AA. Achieving a public health
recommendation for preventing neural tube defects with folic
acid. American Journal of Public Health 1999; 89(11): 1637-40.
7 Wilson RD. The use of folic acid for the prevention of
neural tube defects and other congenital anomalies. Journal
of Obstetrics and Gynaecology Canada 2003; 138: 1-7.
8 Van Allen MI, McCourt C, Lee NS. Preconception Health: Folic
Acid for the Primary Prevention of Neural Tube Defects. A Research
Document for Health Professionals, 2002 (Catalogue H39-607/
2002E) Ottawa: Minister of Public Works and Government
Services Canada, 2002.
9 Morin P, De Wals P, St-Cyr-Tribble D, et al. Pregnancy
planning: a determinant of folic acid supplements for the
primary prevention of neural tube defects. Canadian Journal
of Public Health 2002; 93(4): 259-63.
10 Gucciardi E, Pietrusiak M, Reynolds DL, et al. Incidence
of neural tube defects in Ontario, 1986-1999. Canadian
Medical Association Journal 2002; 167(3): 237-40.
11 Morris JK, Wald NJ. Quantifying the decline in the birth
prevalence of neural tube defects in England and Wales.
Journal of Medical Screening 1999; 6(4): 182-5.
12 Béland Y. Canadian Community Health Survey—
Methodological overview. Health Reports (Statistics Canada,
Catalogue 82-003) 2002; 13(3): 9-14.
13 Rao JNK, Wu CFJ, Yue K. Some recent work on resampling
methods for complex surveys. Survey Methodology (Statistics
Canada, Catalogue 12-001) 1992; 18: 209-17.
14 Rust KF, Rao JNK. Variance estimation for complex surveys
using replication techniques. Statistical Methods in Medical
Research 1996; 5: 281-310.
15 Yeo D, Mantel H, Liu TP. Bootstrap variance estimation for
the National Population Health Survey. American Statistical
Association. Proceedings of the Survey Research Methods
Section. Baltimore, Maryland: August, 1999.
