Responses recorded in this study provide a comprehensive insight into the knowledge and attitude about the metabolism of vitamin D and its physiological role (which is usually formed during the early years of medical school ) among the healthcare professionals in Bangladesh. To the best of our knowledge, this study is among one of the most comprehensive investigations encompassing a diverse population of healthcare providers an also due to its high sample size (n = 2,190). Results of this study highlight that an overall negative attitude towards sunlight exposure could be predominant among some of the medical practitioners in Bangladesh (evident from 68% of respondents believing that regular sunlight exposure in Bangladesh would be harmful contrary to 30% deeming this as good; Fig. 1). This was further evidenced by a high percentage of the respondents identifying skin burn and cancer as potential outcomes of 30-minute daily exposure (45% and 30% respectively; Fig. 1). But, is such a negative attitude among the medical community in Bangladesh supported by strong evidence?
Bangladesh has a subtropical climate where, unlike the tropical countries, sunlight intensity remains relatively mild. The monthly average of the highest daily UV index ranges from 6 to 7 throughout the year which is not as high as it is observed in many other tropical countries . Moreover, this range (6 to 7) reflects the daily highest levels that last for a short duration of a day. Furthermore, the UV index is a physical parameter. Any quantitative measurement of its effects on various aspects of human health depends on other factors (e.g., skin complexion, clothing practices, etc. ). The effect any UV exposure could cause to fair skin in 15 minutes could take up to hours for people with darker skin because of melanin (which is responsible for skin darkness) absorbing the UV radiation [3, 28]. In this regard, the South Asian population has generally dark skin complexion belonging to skin-type IV and V according to the Fitzpatrick complexion scale [29, 30]. This most likely explains Bangladesh ranking 183rd globally on the list for the prevalence of melanoma , and also sunburn is extremely rarely reported in this region. These facts indeed bolster the argument against the hypothesis that the intensity of UV radiation in Bangladesh will have highly negative effects on human health. Therefore, the perception of the level of UV radiation in Bangladesh being 'very harmful' and extrapolating this to conclude that direct sunlight exposure would bring harmful to very harmful effects to human health could most likely be an overstatement. In this regard, further research on the dose-response relationship and quantitative risk assessment in the context of Bangladesh and South Asia could be particularly helpful to gain further insight. But for now, could such a negative attitude among the healthcare providers have larger and more direct implications for the wider community?
Only 22% of the participants of this study identified the time ‘from 10 am to 3 pm as the best time for the production of vitamin D in Bangladesh (Fig. 2), whereas 69% of the respondents believed ‘before 10’ am as the best time. While there is no published literature regarding this timing in the context of Bangladesh (or any neighboring country), the solar intensity in the morning and the afternoon (after 3 pm) remains low to mild due to its mostly subtropical climate . This means UV-B intensity remains very low during this time, which starts getting more intense as it approaches mid-day. Along with this, taking the generally dark complexion of the Bangladeshi population (skin types IV and V) [29, 30], net absorption of UV-B (even after direct exposure) by an average Bangladeshi in the morning would likely be really low. However, this scenario would change around mid-day time (10 am to 3 pm) when the level of UV-B in the sunlight would be maximum. Hence, it is highly likely that this time of the day comprises the best time for the production of vitamin D from direct sunlight exposure, which is also strongly supported by the literature [1, 3, 12]. As such, the hypothesis that the time between sunrise and 10 am is the best time to get vitamin D from sunlight, particularly in the context of Bangladesh, is most likely not correct. While the lack of research data regarding the best time to get vitamin D from sun exposure (preferably across different seasons throughout the year) highlights a significant knowledge gap, the majority of the medical practitioners identifying the wrong time also needs to be addressed.
On a similar note, regarding the minimum weekly duration to get enough vitamin D from sunlight, a clear majority of the respondents (60%) thought < 30 minutes of direct sunlight would be adequate for the Bangladeshi population. While any specific guideline or clear consensus among the researchers is missing in this regard, Holick et al. (2007) suggested 5 to 30 min of sunlight exposure twice a week could often be sufficient . However, this recommendation was based on studies conducted on people with lighter skin completion, and as such, it has been argued later that this could be a significant underestimation for many other populations (as the required weekly exposure could be significantly higher when other aspects like darker skin complexion and clothing practices are considered ). While further research is warranted to determine the minimum duration more precisely, considering the darker skin complexion of the South Asians in general and heavier clothing practices in this region for cultural and religious reasons (like in Bangladesh ), it would be safer to believe that the minimum required weekly exposure would almost certainly exceed 30 minutes. As such, the majority of the healthcare providers thinking (and perhaps communicating with the mass people) that < 30 minutes of weekly sunlight exposure would be adequate is highly likely to be inaccurate. More specific experimental studies for a clearer understanding of the dynamics of serum vitamin D production as a result of sunlight exposure under varying conditions would be highly beneficial in this regard.
However, we hypothesize that the healthcare professionals undermining the necessity for longer duration constitutes a significant source of misinformation for the wider community, which might be one of the contributors to the high prevalence of vitamin D deficiency in Bangladesh and this could be true for South Asia overall [5–7]. The absence of such studies (regarding sunlight and vitamin D) in the other South Asian regions, therefore, represents a key research gap regarding the accuracy of knowledge and attitude.
Among the symptoms of vitamin D deficiency, those having obvious relation to Calcium (Ca) metabolism (like 'bone and waist pain' and bone loss) were more readily identified as the symptoms of vitamin D deficiency, while those having a less obvious connection to Ca-metabolism (like hair loss, tiredness, frequent illness, and depression) were identified by only a small percentage (Fig. 1). A similar trend was observed for the potential long-term effects of vitamin D deficiency; osteoporosis and arthritis were identified by the majority of the respondents, cancer, diabetes, heart disease, hypertension, anemia, obesity, autism, etc. were identified by very few (< 10%) respondents in each case. This leads to a hypothesis that the medical practitioners in Bangladesh might be more focused on Ca-metabolism while the other critical roles of vitamin D might be significantly overlooked. Indeed, this has been reported in studies conducted in other countries as well [18, 35]. So, what might be behind the suboptimal level of knowledge among healthcare professionals in general?
The majority of the respondents (67%) being unaware of the very high prevalence of vitamin D deficiency in Bangladesh as well as in the whole South Asian region across all age groups could be related to this [5–7]. Despite such high prevalence, a general lack of awareness about the seriousness of this problem perhaps explains why only 12% of the healthcare providers have checked their serum vitamin D level ever (Fig. 1).
Finally, taking food that is rich in vitamin D was preferred over regular sunlight exposure as a better intervention to mitigate widespread vitamin D deficiency in Bangladesh (Fig. 1). In this regard, when the poor socioeconomic demography of Bangladesh is considered, taking vitamin D-rich foods in sufficient quantity (yet on regular basis) by the mass people in Bangladesh might be practically challenging for a large portion of the community. Also, focusing mostly on dietary sources for vitamin D can undermine the more sustainable option, since most of the serum vitamin D (as high as up to 90%) is known to be produced in the skin from regular sun exposure only, which is abundant in Bangladesh throughout the year . Furthermore, the vitamin D precursor (25-hydroxy vitamin D) produced from sunlight has a higher half-life compared to when it is absorbed from dietary sources or vitamin D supplements [37, 38]. Therefore, from a more practical perspective, we argue that regular sunlight exposure can be a good, and perhaps sustainable, option at a mass scale for the wider community in Bangladesh and other countries with similar geographic and socioeconomic contexts.
The major focus of our study was how the medical community views the health implications of regular sunlight exposure, particularly in the context of getting vitamin D for individuals and the wider community. Regarding the knowledge related to the metabolism and pathological aspects of vitamin D, our overall findings conform to a handful of other published studies conducted in China, Saudi Arabia, and Pakistan. In Saudi Arabia, a study conducted among general physicians and their findings point out that knowledge and practice need to be improved regarding vitamin D . In China, a study was conducted among medical students and the result showed that there is little knowledge and unfavorable behaviors regarding vitamin D among their study participants . In Pakistan, a study was conducted among medical students and their findings also highlighted the need for improved knowledge about vitamin D and its metabolism among study participants . As such, our study was unique due to it addressing the knowledge and attitude regarding the potential health implication of sun exposure, a much-required practice, particularly in countries with a high prevalence of vitamin D deficiency. Furthermore, this study encompassed a wider spectrum of healthcare providers (from junior to senior level) yet was conducted on a large number of participants.
Due to the major focus of this study being the knowledge and attitude regarding sunlight exposure to getting vitamin D, many of our questions were unique. Therefore, we could not fully compare our participants' answers (regarding sun exposure) to other studies. Despite our best efforts to keep the samples representative (by considering the stratifications that exist), we acknowledge that true randomization could not be achieved. Indeed, a very high number of responses (higher than any other published studies according to the best of the knowledge of the authors) were collected to offset any potential sampling bias. However, caution should still be maintained before generalizing the conclusions for the entire medical community in Bangladesh and beyond.