INTRODUCTION
Vitamin D deficiency (VDD) is a major public health concern [
1]. It is reflected by low serum 25-hydroxyvitamin D (25-OHD) levels, which lead to adverse changes in calcium and phosphate homeostasis and increased fracture risk. In the Philippines, a 2009 study of postmenopausal women found that 36% of the participants had insufficient 25-OHD levels (20-30 ng/mL), but only 30% of those women received calcium and vitamin D supplementation [
2]. Another study of 369 randomly selected Metro Manila office workers in 2014 revealed that 58% of the participants had deficient serum 25-OHD levels (< 20 ng/mL), while 30% had insufficient levels [
3].
Exposure to ultraviolet rays (UVB) is the main source of vitamin D in humans. This is because the enteral route is not a good source of vitamin D unless foods are fortified with vitamin D [
4]. A contributing factor to the increasing prevalence of VDD in the Philippines is rapid urbanization, which has resulted in more young adults having indoor jobs and thus less sun exposure, raising concerns about bone health during the period when they are achieving peak bone mass. Furthermore, air pollution in major Philippine cities decreases the amount of UVB that reaches the earth’s surface [
5].
A major limitation in the area of VDD research is the lack of an appropriate, inexpensive, and easily-administered tool for measuring sunlight exposure [
6]. Compared with other methods, questionnaires are considered to be the most cost-effective way of measuring sunlight exposure in population-based studies [
7]. Of the available sunlight exposure questionnaires (SEQs), only 2 were validated in Asia (Hong Kong and Pakistan) [
6,
7] and only 3 were created in the context of VDD by correlating the questionnaire results with serum 25-OHD levels, showing moderate correlations [
6,
8,
9]. At present, there is no existing SEQ that has been validated for Southeast Asian or tropical populations. This study aimed to develop and validate a culturally-appropriate, self-reported SEQ for urban adult Filipinos.
DISCUSSION
This is the first SEQ developed and validated for use in an urban adult Filipino population. The questionnaire was designed to assess the intensity of sunlight exposure, the various factors affecting sunlight exposure, and the different sunlight protection practices utilized by urban adult Filipinos.
To ensure adequate representativeness of the sample, our sampling frame took into account age, sex, educational attainment, work shift and location, and economic status. Although it could be argued that elderly respondents should comprise a greater proportion of the sample (given that the consequences of VDD are especially strongly felt in this population), our aim was to create a more even distribution of respondents across the entire adult lifespan to maximize the questionnaire’s applicability [
17]. The respondents’ locations within Metro Manila were not part of the sampling frame, since each of the Philippine capital’s 17 component cities are topographically similar, and hence there were no expected significant differences in sunlight exposure. The Köppen climate classification lists Metro Manila as having a uniformly tropical wet and dry climate [
18].
The questionnaire development process drew on the existing instruments of Cargill et al. [
9] in Australia, Hanwell et al. [
8] in Italy, Humayun et al. [
6] in Pakistan, and Wu et al. [
7] in Hong Kong. Although the questionnaires served as important references, no questions were directly taken from any of these instruments, as they were all developed in countries of a different ethnicity, geography, and climate compared to the Philippines. Hence, we utilized a separate conceptual framework that explored additional aspects of sunlight exposure in Filipinos that may not have been covered in the existing questionnaires [
11]. A unique feature of our questionnaire is the inclusion of questions pertaining to the perceived risks and benefits of sunlight exposure, which are significant determinants of an individual’s sunlight exposure practices. We also added questions pertaining to the influences of other people and mass media on sunlight exposure, given the strong kinship and social ties among Filipinos and the widespread use of technology by urban residents [
19]. A current disadvantage of the questionnaire is the lack of a validated scoring system and the lack of correlation with established gold standard measurements, the latter of which will be addressed in the next phase of the study.
In the construction of questionnaire items, we utilized the Likert scale, the most widely-used approach to scaling responses in questionnaire research. Unlike simple close-ended questions, the Likert scale has the ability to specify levels of agreement or disagreement in a symmetric fashion, capturing the range of intensity of feelings for a given item, which is then simplified as the sum of the questionnaire items [
20]. Questionnaires in Likert scale format are also easy to use and allow more variables in a study because the format enables respondents to answer more questions in the same time required to answer fewer open-ended questions [
21,
22]. While we retained the same choices for many questions (“never,” “rarely,” “often,” and “always”), the choices for other questions were crafted to reflect a similarly symmetric degree of sun exposure. This was especially true for questions involving the Fitzpatrick skin classification, body part exposure, and temporal exposure.
During the translation and back-translation process, the independent bilingual translators decided to retain several words in English. This is due to the fact that these particular words are considered familiar terms for ordinary Filipinos. In the 2010 Test of English as a Foreign Language, the Philippines ranked 35th out of 163 countries worldwide, and ranked second-best in Asia after Singapore [
23].
The questionnaire was assessed using content validity, construct validity, and reliability. Content validity, which refers to the representativeness or relevance of the questionnaire content, was assessed individually by the members of an expert panel [
7]. These members were chosen from diverse disciplines to ensure a holistic clinical and psychosocial evaluation of the questionnaire items. While majority of the items possessed sufficient content validity, those that were removed were mostly either redundant or found to be non-contributory to sunlight exposure evaluation. Others (such as the use of sunlamps or sunbeds) were deemed not applicable to Filipino culture.
Our questionnaire also possessed satisfactory construct validity. The 3 domains extracted after factor analysis corresponded well with the themes identified during creation of the conceptual framework. Specifically, the first 2 domains corresponded to the influences and perceived benefits and risks of sunlight exposure. The third domain also corresponded to perceived risks, as an increased awareness of these risks leads to an increased usage of sun protection practices (
Figure 1). Furthermore, the factor analysis results also fulfilled the rule of having a minimum of 5 questions per domain to enable psychometric testing, with 7 questions in the first domain, 12 questions in the second domain, and 6 questions in the third domain [
24]. Reliability, meanwhile, was likewise sufficient in terms of both internal consistency and test-retest reliability. For the latter, the decision to administer the questionnaire 2 weeks apart was made because that time frame was long enough for the participants to not remember their responses from the first test, while being short enough to not allow significant physiological changes to occur. There was also no significant difference in the time needed to complete the first and second rounds of testing, attesting to the questionnaire’s consistency in ease of administration.
This study serves as part of a larger project that will eventually involve concurrent and criterion validity assessment of the questionnaire results with established objective parameters, such as dosimetry and serum 25-OHD levels. We also recommend future studies investigating the applicability of the questionnaire to a wider population, particularly rural and other urban areas in the Philippines, in addition to other Southeast Asian and tropical countries of similar ethnicity and geographical latitude.
In conclusion, this study showed that a linguistically and culturally appropriate SEQ possessed sufficient content validity, construct validity, and reliability to assess sunlight exposure among urban adult Filipinos in Metro Manila. The questionnaire results can be eventually applied to evaluate associations with serum 25-OHD levels.