Vitamin D Status and Usual Nutrient Intake of Filipino Children Aged 6–12 Years in Selected Areas in the Philippines: A 2018 National Nutrition Survey

Background . This study aimed to determine the prevalence of vitamin D deﬁciency, usual nutrient intake, and food sources of vitamin D of Filipino children aged 6–12 years in selected areas in the Philippines. Methods . The National Nutrition Survey (NNS) collected blood samples of children aged 6–12 years from selected study sites: Manila City and Quezon City in the National Capital Region (NCR); Cagayan Province and Baguio City in Luzon; Northern Samar and Siquijor in Visayas; and Butuan City and Sultan Kudarat in Mindanao. About 789 children aged 6–12 years participated in this study. Serum vitamin D was determined by electrochemiluminescence binding assay (ECLIA). Food intake data were collected using two-day nonconsecutive 24 h food recall. Usual nutrient intakes were estimated using Personal Computer Software for Intake Distribution Estimation (PC-SIDE) program. Results . The mean serum vitamin D of 25 (OH)D was 72.7 ± 0.67 μ mol/L. The overall prevalence of combined vitamin D deﬁciency ( < 50 μ mol/L) and insuﬃciency (51–74 μ mol/L) among children aged 6–12 years was 60.6%. Females had a higher prevalence of vitamin D insuﬃciency compared to males. NCR (57.9%) had a higher deﬁciency compared to the other areas. The usual intake of vitamin D (2 μ g/day) among children was below the adequate intake of 5 μ g/day. The main food sources of vitamin D are coming from ﬁsh (53%), pork (19%), and egg/egg dishes (16%). Conclusion . This study revealed that there is a signiﬁcantly high level of vitamin D insuﬃciency in children aged 6–12 years. Filipino females had higher prevalence of vitamin D deﬁciency and insuﬃciency compared to males. Among the areas, NCR has the highest prevalence of deﬁciency/insuﬃciency.


Introduction
Vitamin D, also known as the sunshine vitamin, is essential for the health and growth of bones. It helps the body to absorb calcium from the gut and regulates how much calcium and phosphorus gets stored in the bone. e vitamin D content of the human body is synthesized to 7-dehydrocholesterol (7-DHC) by the exploit of ultraviolet B (UVB) irradiation from sunlight. It is converted to 25-hydroxyvitamin D (25(OH) D) in the liver by hydroxylase and then transported in the kidney forming 1, 25-dihydroxyvitamin D (1, 25(OH) 2 D) by other hydroxylation [1,2].
Vitamin D and calcium are bone growth nutrients. In children, vitamin D deficiency can cause skeletal diseases such as nutritional rickets (NR), osteomalacia, and troubles in calcium homeostasis [3]. Also, the lack of vitamin D has been associated in mental health disorder and can cause neurohormonal effects on brain development and behaviour [4]. Globally, vitamin D deficiency is a major public problem in all age groups even in the countries with more sun exposure all year round [5]. e highest level of vitamin D serum values were observed in North America than in Europe or Middle East/Africa region. However, in the Asia region, children were found to have significantly lower vitamin D serum values than adults and elderly [6].
ere are few foods that naturally contain vitamin D; hence, the amount of time in sunlight is important [7]. A previous study found out that sunlight exposure was thought to directly kill the tuberculosis bacteria [8]. ere have been multiple cross-sectional studies associating lower vitamin D with increased infections. Individuals with less <30 ng/ml of vitamin D levels were more likely to self-report a recent upper respiratory tract infection than those with sufficient levels, even after adjusting the variables of age, gender, season, body mass index, and race [9]. Just at this time of the coronavirus pandemic, numerous news reports considered vitamin D from sun exposure as one of the protective gear against the virus.
Because of the critical role of vitamin D both in growth of children and in immune response, this study aimed to determine the prevalence of vitamin D status, usual nutrient intake, and food sources of Vitamin D of Filipino children, aged 6-12 years in selected areas in the Philippines based on the 2018 National Nutrition Survey data (NNS 2018).

Study Population.
e sampling frame of the 2018 National Nutrition Survey utilized the new 2013 master sample (MS) developed by the Philippine Statistics Authority (PSA). It is a two-stage cluster sampling design with the first stage being the selection of primary sampling units (PSUs) composed of barangays or Enumeration Areas (EAs) or a group of adjacent small barangays or EAs followed by the selection of secondary sampling units (SSUs) composed of housing units or households. Each PSU is composed of 100-400 households. e 2013 MS used provinces, highly urbanized cities (HUCs), and urban areas as its sampling domain. Finally, the NNS patterned the list of households from the 2015 Population Census.
Replicated sampling was employed in the selection of provinces and HUCs in order to gain efficiency in the generation of national-level estimates for a given year. is was carried out by grouping the provinces and HUCs with similar characteristics into "replicates." A replicate is composed of, at least, 5 provinces or HUCs. Compared from the previous surveys, the rolling survey termed as the Expanded National Nutrition Survey (ENNS) has 24 replicates (8 replicates per year) to achieve reliable domain-level estimates. It targets to cover 117 major sampling domains composed of 81 provinces, 33 HUCs (including 16 cities in the National Capital Region); and 3 other urban areas. A total of 40 provinces and HUCs were covered for the year 2018, while another 40 and 37 areas are expected to be surveyed for the subsequent years 2019 and 2020, respectively.
In all the ENNS components, an average of 1536 households were targeted except for the biochemical, dietary, and blood parameters of the clinical component. e target households covered for the two components were only half (50%) or about 768 households. is is due to high cost of laboratory analyses for the biochemical component and a tedious data collection for the dietary survey.
Based from previous NNSs, the number of participating 6-12-year-old children was on the average, ±4,000. Using the critical value of the normal distribution at α/2 (e.g., for a confidence level of 99%, α is 0.01 and the critical value is 2.576) and the proportion of vitamin D deficiency based on the published literature of 40% with an acceptable sample error of 0.05, the calculated sample size is 640 children.
All the 40 provinces covered in 2018 were clustered by region. Each region was then clustered into 3 island groups, namely, Luzon, Visayas, and Mindanao. From each Island group, 2 provinces were randomly selected as the study sites: ese areas were Manila City and Quezon City in the National Capital Region (NCR) as highly urbanized cities; Cagayan Province is second largest region in terms of land area and lies in a large valley in northeastern Luzon; Baguio City is also a highly urbanized city in Luzon. e province of Northern Samar is bounded by the Pacific Ocean on the east; Siquijor is a coastal municipality in Visayas. Butuan City is a coastal, highly urbanized city, and Sultan Kudarat Province is a coastal area in Mindanao.
is study included children aged 6 to 12 years from the 8 study sites. ere were 2782 children who participated in the dietary survey, and 789 children had blood samples for the analysis of serum vitamin D.

Dietary. Two-day nonconsecutive 24-h dietary recalls
were conducted face-to-face with the parent or caregiver of each child. Trained registered nutritionists-dietitians carried out the interviews during household visits using structured questionnaires. To estimate the day-to-day variance component in energy and nutrient intake required for usual intake analysis, the first 24-h dietary recall was collected for all children and a second 24-h dietary recall was repeated in 50% of randomly selected households on a nonconsecutive day. e second 24-h dietary recall was typically collected 2 days after the first 24-h recall. e interviewer asked about all foods and beverages that the child consumed on the previous day. e amount of each food item or beverage was estimated using common household measurements such as cups, tablespoons, by size, or number of pieces. e information was then converted to grams using a portion to weight list for common foods compiled by the Department of Science and Technology-Food and Nutrition Research Institute (DOST-FNRI) or through actual weighing of the food samples.

2.2.2.
Biochemical. Blood samples were obtained in the morning (0600H to 0900H) via venipuncture. Precautions were considered throughout the procedure to minimize exposure of samples to air and light. Approximately, 10°mL venous blood samples to accommodate all the biomarkers needed for the survey was extracted using a sterile syringe and transferred to a blue top tube. After a marked separation of serum and red cell was seen, the tube was centrifuged for 10 minutes. Serum was pipetted into microcentrifuge tubes. All serum were kept in freezers or in ice chests with dry ice. Frozen blood samples were transported to the Biochemical Laboratory (BL) of DOST-FNRI where these were stored in freezers at −80°C until analysis. e best indicator of vitamin D status is the serum 25hydroxyvitamin D (25(OH)D) concentration [10]. Total serum 25-hydroxyvitamin D ((25-OH(D)) was analyzed using the electrochemiluminescence binding assay (ECLIA) method in a selected ISO 15189 accredited laboratory in Metro Manila. e cutoffs for vitamin D levels are deficient (<50 nmol/L), insufficient (51-74 nmol/L), and sufficient (≥75 nmol/L) [2,11].

Data
Processing. Food records were encoded, and estimated vitamin D intakes were processed with a computer system called the Individual Dietary Evaluation System. is system contains the data of an updated Filipino Food Composition Table (FCT) created and used in previously published studies. e updated FCT contains 27 nutrients from 1359 foods. About half of the data (47%) were from the United Sates Department of Agriculture (USDA) national nutrient database, and 39% of the data were from the original Filipino FCT compiled by the FNRI [12]. e rest of the data were sourced from the food composition database of Association of Southeast Asian Nations and other Asian countries such as Japan (8%) and information from food labels (6%). All imported data were adapted according to the International Network of Food Data Systems guidelines Food Agriculture Organization [13].
Quality control of the dietary intake data was conducted in two steps. In the first step, the foods reported by a participant were reviewed and information including coding and quantity reported were screened and validated. In the second step, vitamin D intakes were reviewed to identify implausible values by using the method described by Lopez-Olmedo et al. [14]. For implausible micronutrient intakes, excessive intakes were defined as those that exceeded 1.5 times the 99th percentile of the observed intake distribution of the nutrient in the corresponding sex and age group. Intakes above the upper limit were substituted by a random value generated from a uniform distribution in the intervals with the lower bound equal to the 95th percentile of the observed intake and an upper bound equal to 1.5 times the 99th percentile [14].
To investigate food groups consumed and food sources of vitamin D, a list of 80 food groups was used in a similar format from previous dietary intake studies in young children [15] (Table 1). Data analyses for food groups consumed and sources of vitamin D intake were based on the first 24-h dietary recall. All foods and beverages reported were assigned to one of the 80 food groups.

Statistical Analysis.
e Software of Intake Distribution Estimation (PC-SIDE) was used to estimate the distribution usual energy and nutrient intakes and prevalence of inadequate intake. e PC-SIDE software follows the Iowa State University (ISU) method which adjusted the daily intake to remove the effect of within-person variability, so that the estimated distribution has a variance that reflects only between-person variability. Evaluations of vitamin D were assessed against the Adequate Intake (AI) by comparing results to the Philippine Dietary Reference Intake [16].
Food group consumption (i.e., percent consuming) was expressed as the percentage of children/mothers who consumed specific food groups, at least, once on the first 24-h dietary recall regardless of the amount consumed. is method has been used in our previous studies. e weighted percentage contribution of each food group for selected key nutrients was calculated by adding the amount of a given nutrient provided by each food group for all individuals and dividing by the total intake of that nutrient consumed by all individuals from all foods and beverages.
Stata (Stata Statistical Software, release 15, Stata Copr. 2017) was used to calculate the contribution of each food group to the total vitamin D intake. Independent t-test was used to test the difference of mean vitamin D intake for two groups. One-way ANOVA with Bonferroni multiple comparison adjustment was used to test the difference of mean vitamin D intake for more than two groups. e chi-square test was conducted to test the association between vitamin D and the characteristic of the population. Table 2 presents the characteristic of subjects and the distribution of usual vitamin D intake. e average age of 6-12years-olds is 9.4 years. For boys, their average age is 9.5 years, and for girls, it is 9.4 years. ere is a similar percentage of boys and girls in the study. Sixty-four percent of the children were from rural areas. About 17%, 20%, 31%, and 32% of the children were from NCR, Luzon, Visayas, and Mindanao, respectively. Approximately one quarter (26%) of the participants were classified as rich, while the other 36% and 38% were classified as middle and poor, respectively. Twenty-five percent (25%) of the participants were stunted. e average vitamin D intake was 2.0 mg/d. Girls have slightly higher intake of vitamin D compared to boys. Children from rural areas have significantly higher intake of vitamin D than those from urban areas. Children from Luzon have significantly higher intake compared to those from the other islands. Children from wealthy family have significantly higher consumption of vitamin D. Stunted children have significantly lower intake of vitamin D compared to those who are not (Table 2).

Results
In Table 3, children's vitamin D intake was categorized into 5 groups (Q1, Q2, Q3, Q4, and Q5). Each group represents 20% of the total sample. e chi-square test showed that urbanity, island group, wealth status, and stunting were significantly associated to vitamin D quintiles. Table 4 presents the distribution of serum concentration of 25(OH)D of 6-12-year-old children. e average serum concentration of 25(OH)D was 72.7 nmol/L. Boys have higher vitamin D level than girls. Children from rural areas have higher vitamin D level compared to those from urban areas. Children from NCR have the lowest vitamin D level compared to those from other areas. About 60.6% have deficient and insufficient of vitamin D concentration. Sex, urbanity, island, and stunting status were associated to vitamin D status (Table 5).

Discussion
is study was conducted primarily to analyze the status of vitamin D, usual intake, and its food sources among children aged 6-12 years who participated in the 2018 NNS conducted by the Department of Science and Technology-Food and Nutrition Research Institute (DOST-FNRI). Only 8 randomly and geographically selected areas in NCR, Luzon, Visayas, and Mindanao were considered in this analysis. e sun is the best source of vitamin D; hence, nonexposure to sunlight leads to decreased vitamin D synthesis.
e Philippines has plenty of sunlight, but vitamin D deficiency (10.3%) and insufficiency (50.3%) is very high among the 6-12-year-old children. However, our result is lower than the prevalence in Indonesia among children aged 7-12 years, wherein the prevalence of vitamin D deficiency was 15% and insufficiency was 75.8% [17]; also, a higher prevalence of vitamin D deficiency (59.1%) among schoolchildren in Busan was reported [18].
e National Capital Region has the highest prevalence of deficiency (30.1%) and insufficiency (57.9%) which is significantly higher than that of the three island groups. A similar result was found in our previous study of vitamin D deficiency among adults in the Philippines. NCR has the highest prevalence of vitamin D insufficiency compared to Cebu (located in Visayas) and Davao (located in Mindanao) [19]. is could be attributed to differences [20]. Although our the previous study was among adults who have different body frame and biological nutrient metabolism than our study children in this present study, we believe that geographical location could be a prime factor. NCR is a highly urbanized area and is the center of commerce, employment, and education. It has limited space, so people including children tend to spend more time indoors. Furthermore, in NCR, children go to classes early in the morning at 6:00 AM and go home at around 12:00 noon. Since NCR is a metropolitan area equipped with the different gadgets and electronic devices, children tend to stay inside the house to play computer games or watch TV. Time outside home to get sunlight is very limited. In a previous study, children who watched more TV, played less outside, and used less biking    Journal of Nutrition and Metabolism to school were associated with higher risk of vitamin D deficiency [21]. is scenario may also be true in other urbanized cities or cosmopolitan areas. In has been postulated that urbanity is associated to increase in indoor lifestyles and regular use of sunscreen. is might be the reason why there is a high prevalence of vitamin D deficiency and insufficiency found in our children in urban areas as compared to those living in rural areas. High prevalence of vitamin D deficiency in the urban area was also reported in Turkey [22], and China [23]. Additionally, a communitybased study showed that the prevalence of vitamin D deficiency among Indians living in urban areas ranged from 50% to 94% [24]. e girls in this study have higher prevalence of vitamin D deficiency (11.9%) compared to boys (8.9%) using the cutoffs for vitamin D deficiency as <50 nmol/L. In a study among children aged 6-18 years, about 93% were vitamin D deficient (using cutoff value as serum 25 hydroxy D < 20 ng/ ml), and the prevalence among female children was higher than that among men because most men have a higher sun exposure than females due to more outdoor lifestyle and activities as they have more freedom [25]. A high prevalence of vitamin D deficiency and insufficiency (65.1%) among healthy adolescents in United Arab Emirates was also more common in females [26]. e main reason that a female has low vitamin D serum was the difference in the amount of subcutaneous fat between genders. Females have more subcutaneous fat than males [27]. It has been hypothesized that more amount of subcutaneous fat in females could take up more vitamin D particles produced from the skin that could lead to lower vitamin D particles entering in the blood circulation [28]. Moreover, lifestyle differences between females and males could give difference in vitamin D status. Females more often use sunscreen when they are outdoors. e usual intake of vitamin D among Filipino children was 2.0 µg per day which is below the recommended intake per day of 5 µg in children (PDRI 2015). is is obviously too low to influence 25 (OH)D levels of the children. e Institute of Medicine (IOM) recommends a daily intake of vitamin D of 400 international units (IU) or 10 μg daily and the tolerable upper limit of 2000 IU daily or 50 μg [29]. Moreover, it has been reported that, to raise the serum 25(OH)D to over 75 nmol/L, a daily intake of 1000-2000 IU is required [30]. Lack of vitamin D intake can cause softening and weakening of bones of children known as rickets due to poor mineralization and may stop them from reaching their genetically programmed height and great bone mass [31]. is might be the reason why the country is facing the problem of stunting among our children. Moreover, it has been found in a recent prospective, double-blind placebo study that vitamin D has resulted in a significant decrease (42%) in the incidence of influenza infection [32]. is is because of the role of Vitamin D in suppressing the development of cytokine by simultaneously boosting the innate immune system to respond to the viral load immediately. Some researchers also indicated the possible involvement of vitamin D during the 1918-1919 viral influenza pandemic in suppressing cytokine storms [33]. Most importantly, vitamin D is very important in enhancing the immune response of flu and previous coronaviruses [8,34] because of its ability in suppressing cytokine production [35]. It is in this notion that, during this time of the coronavirus pandemic (COVID-19), increasing vitamin D intake or exposure to sunlight could be very beneficial to squash the cytokine storm occurring during the attack of COVID-19.
Major food sources may differ in other countries. In this study the main food sources of vitamin D among children are fish (53%), pork (19%), and egg/egg dishes (16%). In the United States, their main sources of vitamin D are milk, cereal, and fish [36]; in Japan and the United Kingdom, fish is their main food source of vitamin D which is similar to our study [37,38]. High consumption of fish can help increase serum concentration of 25(OH)D [39]. It has been reported that regular consumption of fish is associated with a higher vitamin D intake [40]. However the amount of intake of these vitamin D-rich foods in our children in this study is very limited (fish (41 g), pork (22.1 g), and eggs/egg dishes (27.7 g)).
e study is only limited to the comparison of Vitamin D serum level in Filipino schoolchildren aged 6-12 years. Variables such as duration of sun exposure and time of the day during sun exposure were not evaluated.

Conclusions
e prevalence of vitamin D insufficiency among Filipino children 6-12 years is significantly high (50.3%). Females have a higher prevalence of vitamin D deficiency and insufficiency compared to the males. NCR has the highest deficiency compared to the other areas. e usual intake of vitamin D is only 2 µg/day which is far below the recommended dietary intake of 5 µg/day. e main food sources of vitamin D in this group of children are fish, pork, and eggs/ egg dishes, but these were consumed in limited amounts. It is highly recommended to have outdoor activities and increase the vitamin D intake of school children to contribute to addressing stunting and improving immunity.
Data Availability e data in this study are not available for public use because of the confidentiality agreement between the researchers and the respondents' parents as stipulated in the Ethics Protocol of Food and Nutrition Research Institute.

Conflicts of Interest
e authors declare no conflicts of interest.