Journal of the American College of Nutrition, Vol. 18, No. 2, 122-126 (1998)
Published by the American College of Nutrition
Perinatal Vitamin D and Calcium Status of Northern Canadian Mothers and Their Newborn Infants
Barbara Waiters, Bsc, RD,
John C. Godel, MD and
Tapan K. Basu, PhD, FACN
Departments of Agricultural, Food and Nutritional Science, and Pediatrics, University of Alberta, Edmonton, Alberta, CANADA
Address reprint request to: T.K. Basu, PhD, FACN, Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, CANADA
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ABSTRACT
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Objective: This study was undertaken to examine the vitamin D and calcium status of mothers and their newborns.
Methods: The intakes of vitamin D and calcium were determined prenatally in 121 women including 33 Caucasians, 51 Inuits, and 37 Native Indians, living in the Inuvik zone of the Northwest Territories. Plasma concentrations of 25-(OH)-D and calcium were also measured in mothers as well as in their offspring at delivery.
Results: The daily mean vitamin D intake of native mothers, including Inuits and Indians, with (8.1±5.5 µg) and without supplements (3.4±2.5 µg) was significantly lower than that of non-native mothers (13.2±5.9 µg and 5.8±4.3 µg, respectively). According to the predicted prevalence of low vitamin D intake, there existed a higher risk of vitamin D deficiency without supplementation in both native (88.6% vs 48.4%) and non-native (63.5% vs. 15.1%) mothers. The trend for calcium intakes with and without supplementation was similar to vitamin D intake. At the point of delivery, the plasma levels of 25-(OH)-D were lower in native mothers (50.1±19.3 nmol/L) and their offspring (34.2±13.1 nmol/L) than their counterparts (59.8±29.4 nmol/L and 41.4±23.5 nmol/L, respectively). Its plasma levels in newborn infants averaged only 67% of their mothers. None of these infants showed clinical evidence of vitamin D deficiency. In fact, their plasma calcium levels were significantly higher than their mothers.
Conclusions: Plasma 25-(OH)-D concentrations of 60 to 70% of maternal levels may represent a "normal" range for newborn infants. However, a supplementation in native northern Canadian mothers during pregnancy and in their neonates during infancy may have a role to play in the prevention of vitamin D deficiency.
Key words: Northern Canadians, Native Indians, Inuits, Caucasians, mothers, newborns, vitamin D, calcium, 25-(OH)-D
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INTRODUCTION
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Vitamin D is essential for the maintenance of a healthy skeleton throughout our lives [1]. Its daily requirement, has been a subject of controversy. For adults exposed to adequate sunlight, the latest recommended intake is 2.5 µg in Canada [2] and 5.0 µg in the US [1]. During pregnancy the daily recommended intake of vitamin D remains to be 2.5 µg in Canada [2], whereas in the US, it is increased to 10 µg [3]. Since a primary source of the vitamin is believed to be the sunlight, its dietary recommendations vary for populations not exposed to sufficient sunlight. Some recommend 15 µg/day [1], while others have estimated that 12.5 µg/day is sufficient in the absence of sunlight [4]. Few studies have evaluated the vitamin D status of native and non-native individuals living in Northern Canada where sparse or no sunlight along with cold temperatures can severely limit the exposure of these individuals to ultraviolet light and subsequent production of vitamin D in the body. The Canadian Pediatric Society [5] has recommended that pregnant and nursing mothers in the north should take 10.0 µg of this vitamin daily. Studies among native Canadians in Alberta have, indeed, found low intakes as well as low plasma concentrations of several micronutrients including vitamin D [6–10].
Vitamin D, once produced in the skin or ingested in a diet, undergoes hydroxylation in the liver to 25-(OH)-D, which is the major circulating form of the vitamin. In this study, we have examined the influence of dietary vitamin D and calcium as well as their supplemental intakes, on the plasma 25-(OH)-D concentrations of the mothers living in Northwest Territories (NWT). This study was also designed to determine whether or not plasma levels of 25-(OH)-D differ in between native and non-native mothers as well as between mothers and their newborns.
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METHODS
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Subjects
The study was carried out in the Inuvik zone of the NWT as part of the Northern Infant Nutrition Project [11,12]. Included were 121 women from 10 communities along the Mackenzie river and the Arctic coast, enrolled at the time of presentation for prenatal care. Three racial groups were identified on the basis of a questionnaire and of the NWT health care number. Subjects included 51 Inuit, 37 Native Indian and 33 Caucasian mothers. Excluded were women who chose not to consent and those with a history of severe medical problems. The experimental design was approved by the Ethics Committee of the Faculty of Medicine of the University of Alberta.
Each mother was seen two times; first during 1 to 8 months of gestation (mean 4.3 months) and a second time at delivery. At each visit, a dietary history was obtained, and a questionnaire detailing lifestyle was completed. Venous blood was collected from the mothers, while cord blood (mixed) was drawn from the newborns at delivery. All blood samples were collected in heparinized tubes, and the separated plasma samples were stored at -40°C until analysis.
Dietary Assessment
Dietary intakes of calcium and vitamin D at the prenatal visit were assessed by means of two dietary recall assessments complemented by a food frequency questionnaire developed. The questionnaire was based on Native Foods and Nutrition [13] and the list of local foods was verified with the help of local inhabitants and a Nutritionist in Inuvik. The amount of food consumed was estimated on three occasions by a dietitian or a nurse trained in the technique of using food models. Each food was subsequently coded using the code numbers from two publications on native foods [13,14]. Nutrient intake analysis was processed using the 1985 extended version of Canadian Nutrient File [15]. The vitamin D intake was compared with the recommendations (10 µg/day) of the Canadian Pediatric Society for pregnant and nursing women [2]. The probability that intakes were deficient using these levels of recommended intake were calculated using a theoratical method developed by Beaton [16].
Prenatal vitamin D and calcium supplements suggested in this population included 10 µg/day and 1200 mg/day, respectively, as part of the formulation. Information regarding compliance obtained in the questionnaire gave a basis for estimating the actual amount of supplement taken.
25-(OH)-D Analysis
Plasma 25-(OH)-D concentrations were determined by extraction with acetonitrile and subsequent analysis by competitive binding assay [17]. With this method, the minimum detectable limit was 0.17 ng/mL (44.2 nmol/L).
Statistical Analysis
Statistical analysis was carried out using CSS-statistical software [18]. ANOVA, Pearson correlation and multiple regression techniques were used where appropriate. Data in text, figures and tables are presented as means±SD. Procedures were followed which were in accord with standards of the Ethics Committee of the University of Alberta.
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RESULTS
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The mean daily dietary vitamin D intake for both native and non-native mothers living in Northern Canada was 4.2 µg±3.6 (Table 1). The vitamin intake of Caucasian mothers (5.8±4.3 µg/day) was significantly higher than that of either Inuit (3.2±2.5 µg/day) or Indian (3.7±2.5 µg/day) mothers. The total vitamin D intake including supplementation was markedly increased in all three groups; the difference between the groups, however, remained unchanged. Thus, a significant difference in the total vitamin D intake was found between the non-native and native mothers. The daily calcium intake from either diet alone or in combination with calcium supplement, was in parallel with the intake of vitamin D (Table 1). The mean daily calcium intake before or after supplementation, was thus significantly higher in Caucasian than in either Inuit or Indian mothers.
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Table 1. Mean (±SD) Daily Intakes of Vitamin D and Calcium Among Native and Non-Native Mothers Living in Northern Canada1
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Using the Beaton’s method [16] and the recommended daily intake of vitamin D being 10 µg, the calculated risk of the vitamin deficiency for the entire group was 80.8%, and for the Caucasians, Inuits and Indians the predicted prevalence of deficiency was 63.5%, 89.9%, and 87.4%, respectively (Table 2). When supplementary vitamin D was included in the calculation, the risk for deficiency was decreased to 39.0% among the whole group, and 15.1%, 45.0%, and 52.8% among the Caucasian, Inuit, and Indian mothers, respectively. Like vitamin D, the calculated risk of calcium deficiency was markedly less among the non-native than the native mothers; this was true with or without the supplementation.
Table 3 shows the plasma concentrations of 25-(OH)-D and calcium in mothers and their newborns at delivery. The mean plasma levels of 25-(OH)-D were significantly higher in Caucasian than either Inuit or Indian. The plasma calcium levels remained similar in all three racial groups. It was of interest that the plasma 25-(OH)-D concentrations in all infants were 60 to 71% of their mothers’ values. The supplemental intake of vitamin D did not alter the mother vs infant differences in terms of their plasma concentrations of either 25-(OH)-D or calcium (Table 4). The plasma vitamin D metabolite levels of newborns at delivery were significantly higher than that of the mothers in all three groups of study subjects (Table 3). The plasma calcium concentrations, however, were higher in all three groups of newborns than their corresponding mothers; although the difference was at a statistically significant level (p<0.01) only in the Inuit groups.
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Table 4. Effect of Maternal Supplemental Intakes of Vitamin D During Pregnancy on Their Own as Well as Their Newborns’ Plasma Levels of 25-(OH)-D and Calcium at Delivery1
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Significant correlations were found between vitamin D intake during pregnancy and the plasma 25-(OH)-D concentrations of the mother (r=0.29, p=0.002) at delivery. Six percent of the mothers, mostly natives, and majority of the newborns from all three racial groups had plasma 25-(OH)-D concentrations below normal (30 nmol/L).
The infant and maternal plasma concentrations of 25-(OH)-D by month of delivery is shown in Fig. 1. The lowest mean maternal and newborn concentrations were found in late spring and early summer lagging the limited amount of sunlight by about 6 months possibly reflecting sunlight exposure during pregnancy. The mothers’ 25-(OH)-D plasma concentrations found in five of the other 11 months of the year. Newborns 25-(OH)-D levels were also significantly higher in February than every month of the year except the months of May and October. A negative correlation approaching statistical significance was observed between maternal 25-(OH)-D concentrations at the time of delivery and hours of bright sunshine (r=-15, p=0.07). Similarly, a significant negative correlation was observed between plasma calcium level and the number of hours of bright sunshine (r=0.23, p=0.02). Infant plasma calcium concentrations showed no significant relationship to the hours of bright sunshine.
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Fig. 1. Mean plasma 25-hydroxy vitamin D levels in mothers and newborns by month of delivery and hours of sunlight.
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DISCUSSION
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The recommended intake of vitamin D in pregnant and lactating women is subject to controversy. According to many reports [5,8,10,19,20], an intake above the recommended nutrient intake is essential in geographic locations, where days are short and cold for several months in the year and exposure to sunlight is a limiting factor. Many also believe that vitamin D supplementation is required in these situations [10,19].
In the present study the mothers living in the Northwest Territories had daily intakes of vitamin D and calcium well below the recommended levels of 10 µg and 1200 mg, respectively. The intake levels were significantly lower in the native than in the Caucasian mothers. When the supplemental intake of the nutrients was taken into account, the levels of both the vitamin and the mineral were markedly increased but still remained below the recommended levels, especially in the native mothers.
Native women live in remote communities where vitamin D and calcium fortified foods such as margarine, cereal and dairy products are not readily available. Native studies in Northern Canada have shown that financial resources, geographic location, and personal food choices are definite factors affecting vitamin D intake [6–8].
When assessing vitamin D status the most noted biochemical indicator is the circulating concentration of 25-(OH)-D [21]. The plasma level of this vitamin D metabolite was significantly correlated with the total vitamin D intake in mothers at delivery. These results are in agreement with others [19], who reported a similar correlation in a select group of Pakistani women living in Oslo, who were exposed to a very little sunlight.
Six percent of the mothers and a substantial proportion of infants living in the Northwest Territories had levels of plasma 25-(OH)-D below 30 nmol/L, indicating risk of vitamin D deficiency. Indeed, vitamin D deficient rickets have been reported to be a concern among infants living in Northern Canada [9,10]. Thus, between 1972 and 1984, 48 cases (83% native) of rickets were documented at Winnipeg Children’s Hospital [10]. These children lived in the Island Lake area of Northern Manitoba, and they ranged in age from 1 to 49 months.
The plasma concentrations of 25-(OH)-D at delivery were significantly higher in Caucasian mothers and their offspring than the native counterparts. Hollis and Pittard [22] also observed significant racial differences in vitamin D status between white and black mothers as well as their infants, residing in a Northern city. The racial difference in biochemical status of vitamin D is essentially the reflection of the differences in vitamin D intake. Prenatal supplementation with the vitamin resulted in an elevation of the maternal plasma level of 25-(OH)-D, but not in the newborns. These findings are in parallel with others who demonstrated that at term the plasma levels of 25-(OH)-D was significantly increased in mothers supplemented with vitamin D (25 µg/day) in their third trimester of pregnancy [23].
In the present study the newborns’ plasma concentrations of 25-(OH)-D were significantly lower than those of their mothers, averaging only 67% of maternal concentrations. Native infants averaged 66.5% of maternal concentrations compared to 69.2% for their non-native counterparts. These infants were full term, had no signs of vitamin D deficiency, their plasma calcium levels were, in effect, significantly higher than their mothers, and their plasma levels of 25-(OH)-D were not altered by mothers’ supplemental intake. These results are in agreement with others who found that majority of neonates had low plasma 25-(OH)-D concentrations compared with their mothers but had no other biological sign of vitamin D deficiency [21]. These factors suggest that the plasma vitamin D metabolite concentrations of 60 to 70% of maternal levels may represent normal range for newborn infants. It is also noteworthy that in relation to vitamin A, its normal plasma concentration of newborn infants have been suggested to be 50 to 60% of the maternal level [24]. Considering these findings it seems likely that neonates should have a different standard of "normal" than adults, especially for the fat soluble vitamins.
In conclusion, the vitamin D and calcium intakes of northern Canadian women, especially native, are often deficient during pregnancy, and supplementations of these nutrients during the period may be desirable. It is important that a different neonatal standard of "normal" for the plasma 25-(OH)-D level than adults be established. Without these standards, it is difficult to relate mothers’ vitamin D status to their newborn infants.
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ACKNOWLEDGMENTS
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Supported in part by grants from National Health Research and Development Program (NHRDP), Health Canada.
Received June 1, 1998.
Accepted August 1, 1998.
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ABSTRACT
INTRODUCTION
