Prevalence and correlates of folic acid supplement use in Canada
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Folate, one of the B-vitamins, is a key nutrient in reducing the risk of neural tube defects.1 It plays an important role in metabolic pathways that involve vitamin B12 and homocysteine.1 While folate occurs naturally in many foods, such as dark green vegetables and legumes, the most common synthetic form in fortified foods and supplements is folic acid. Members of the general population do not commonly need supplemental folic acid unless it is recommended by a health care professional for certain medical conditions. In fact, high levels of supplemental folic acid may mask and exacerbate vitamin B12 deficiency, particularly in the elderly, which could result in neurological damage.2-4
According to the Institute of Medicine's Dietary Reference Intakes, the Recommended Dietary Allowance for the population older than age 13 is 0.4 mg of folate a day.5 For women of childbearing age, an additional 0.4 mg per day from supplements or fortified foods is recommended.5 Because up to 50% of pregnancies are unplanned, and many women of childbearing age report irregular or no consumption of folic acid before pregnancy, in 1998, Canada approved folic acid fortification of white wheat and other selected grains, in addition to previously implemented supplementation recommendations.6
This analysis uses data from the 2007 to 2009 Canadian Health Measures Survey (CHMS) to investigate self-reported intake of folic acid-containing supplements (see The data). Associations with socio-demographic, behavioural and clinical factors were studied, including, for the first time in a nationally representative sample, red blood cell folate concentrations.
One in four
Results from the CHMS show that one in four Canadians aged 6 to 79 (an estimated 25%) reported taking a supplement containing folic acid in the previous 30 days (Table 1). This figure is consistent with data from the 2004 Canadian Community Health Survey, cycle 2.2 (Nutrition).25 Females were significantly more likely than males to report taking a supplement that contained folic acid (28% versus 21%).
The use of folic acid-containing supplements was highest in the youngest and oldest age groups, and lowest among teenagers and young adults. The greater likelihood of folic acid supplement use among females than males prevailed in age groups older than 30 (data not shown). Use peaked among women older than age 70 (36%) and was lowest among boys aged 14 to 18 (11%) (data not shown).
A positive gradient by household income emerged, with those in the lower income quartiles being significantly less likely than those in the highest quartile to have taken a supplement containing folic acid.
Even when the potential influence of age and household income was taken into account, females were significantly more likely than males to have consumed a folic acid-containing supplement (OR: 1.53; CI: 1.22, 1.92). Household education and country of birth were not significant correlates of folic acid supplement use.
Diet, exercise and smoking
Together, grains and fruit and vegetables are responsible for 62% to 78% of Canadians' dietary folate intake.10,26,27 However, people who ate fruit and vegetables relatively infrequently (less than once a day), had significantly low odds (OR: 0.43; CI: 0.33, 0.57) of taking a supplement that contained folic acid, compared with people who ate fruit and vegetables three or more times a day. Grain intake was not significantly related to folic acid supplement use (Table 1).
People who reported inactive leisure time had significantly low odds of taking folic acid supplements, compared with those whose leisure time was active. As well, the odds of folic acid supplement use were significantly low for daily smokers, compared with people who had never smoked. Having a family physician and the frequency of alcohol consumption were not related to the use of folic acid-containing supplements (data not shown).
The odds of taking a supplement that contained folic acid were significantly low for people whose BMI put them in the overweight/obese category.
Red blood cell folate is the best indicator of tissue folate stores.28 People whose red blood cell folate concentrations were below the median (less than 1,248 nmol/L) were significantly less likely to report taking a folic-acid containing supplement (OR: 0.33; CI: 0.25, 0.43) than were people whose concentrations were at or above the median.
The Tolerable Upper Limit for folate is 1,000 µg of the synthetic form a day. Higher amounts may mask a vitamin B12 deficiency.5 Overall, 17.4% of folic acid supplement users consumed 1,000 µg or more (Figures 1 and 2). Canadian prenatal nutrition guidelines and federal natural health product regulations29,30 support the combined use of vitamin B12 and folic acid supplements to reduce the risk of masking a vitamin B12 deficiency. A large majority (91%) of CHMS respondents who took a folic acid-containing supplement also reported taking a supplement that contained vitamin B12. Further, individuals with low serum vitamin B12 concentrations were less likely to have consumed a folic acid-containing supplement (OR: 0.33; CI: 0.24, 0.47) than were people whose vitamin B12 concentrations were higher.
High plasma homocysteine concentrations are a biomarker for low concentrations of both folate and vitamin B12.20 Individuals with high homocysteine concentrations were less likely to consume folic acid-containing supplements (OR: 0.33; CI: 0.22, 0.52) than were those whose plasma homocysteine concentrations were in the normal range.
The clinical risk factor variable was not significantly correlated with folic acid-containing supplement use (data not shown).
The amount of folic acid in the supplements used by about half (51%) of supplements takers ranged from 400 to 999 µg, and for another third (32%), the folic acid dose was 1 to 399 µg (Figure 1). The remaining 17% took supplements that contained 1,000 µg or more of folic acid: 22% of females and 10% of males.
The most common dose of folic acid for children and teenagers aged 6 to 18 was 1 to 399 µg (Figure 2). Folic acid-containing supplements designed for Canadian children contain 100 to 400 µg.7 At older ages, particularly 51 to 79, the dosage most frequently reported was 400 to 999 µg. Around 20% of people older than 19 reported taking supplements containing at least 1000 µg of folic acid. Such high intake was extremely rare at younger ages.
The use of folic acid-containing supplements is associated with a number of factors: socio-demographic (sex, age, household income), behavioural (frequency of consumption of fruit and vegetables, physical activity, smoking, overweight/obesity) and clinical (blood concentrations of RBC folate, serum vitamin B12 and plasma homocysteine). The results in this overview can inform fortification and supplementation policy in Canada.
The authors thank the Health Analysis Division at Statistics Canada, in particular, Tracey Bushnik and Michelle Rotermann, for their support during the analysis stage of this research. We further thank the Physical Health Measures Division for preparing and granting special access to the data. This research was supported by a CIHR Health Professionals Fellowship in the Area of Public Health to Cynthia Colapinto (funding reference #180375) and a CIHR Operating Grant (funding reference #218776).
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