Vitamin D is critical for bone, teeth and muscle health (Pilz et al 2019); it also has an impact on immunity and the severity of Covid-19 (Deluca 2004; Burchell et al. 2020; Abdrabbo et al. 2021).
Vitamin D deficiency is highly prevalent worldwide (Lips & Van Schoor 2011; Pludowski et al. 2022) and the UK (Hirani et al. 2009; Lips et al. 2020). South Asians are known to have much lower vitamin D levels compared to the white population (Kift et al. 2013; Darling et al. 2018; Darling 2020), with women being at much higher risk (Kift et al. 2013; NICE 2014; Darling 2020).
Vitamin D is primarily produced from exposure to sunlight, and dietary intake can be inadequate (Burchell, et al. 2020; Butriss et al. 2021; Jin 2021).
Skin type affects the absorption of vitamin D as, the darker the skin, the higher the level of melatonin which inhibits the production of vitamin D (Burchell et al. 2020). This means that South Asian populations living in temperate regions such as the UK are at increased risk of vitamin D deficiency (Lowe & Bhojani 2017; Burchell et al. 2020). This is exacerbated if women dress modestly for religious or cultural reasons (Ojah & Welch 2012; Buyukuslu et al. 2014).
The South Asian population includes people of India, Pakistan, Bangladesh, Sri Lanka, Nepal and Bhutan. However, much of the research into these populations fails to take into account the significant differences within the South Asian population. For example, the Bengali population traditionally eat a fish-based diet which may be higher in vitamin D, whereas South Asian people of Indian origin mainly have a vegetarian diet (Darling 2020).
A further difference between the South Asian populations is socio-economic deprivation, with 28-31% of Bengali and Pakistani populations living in the poorest neighbourhoods in the UK compared with 8-9% of the Indian population (Ministry of Housing, Communities and Local government (2020). Socio-economic deprivation is associated with vitamin D deficiency (Lin et al 2021). Evidence also suggests that knowledge of vitamin D varies across participants from South Asian origin (Kotta et al. 2015; Webb et al. 2016; Clark et al. 2019; O'Connor et al. 2018; Burchill et al. 2020).
1.1 Background to the study
NICE (2021) recommends that people with dark skin of a South Asian origin, and those who usually dress modestly when outdoors, should supplement with 10 micrograms of vitamin D daily throughout the year, and this should be made available through outlets such as GP surgeries; health professionals should also promote vitamin D supplementation behaviours. Spending by GP practices on vitamin D supplements has risen from £28 million in 2004 to £76 million in 2011 (NICE 2020). However, in North West London where the first author is based, local prescribing guidance advises primary health practitioners to recommend that patients buy vitamin D supplements over the counter as part of national guidance to reduce costs (NHS England 2022).
1.2 Aim
The aim of the study was to provide an in depth understanding of the factors that influence vitamin D supplementation in women of Bengali origin.
1.3 Objectives
2. Methods
2.1 Study design
We followed the Consolidated Criteria for Reporting Qualitative Research (COREQ) Checklist (Tong et al, 2007) to design and report this qualitative study, aiming to provide an in-depth understanding of perceptions and experiences of vitamin D supplementation in women of Bengali origin attending a general practice in London. The methodological approach entailed one-to-one semi-structured interviews, which were instrumental in harvesting rich, qualitative data reflective of participants' lived experiences.
2.2 Theoretical Framework
The study adopted the COM-B framework (Michie et al. 2011) to provide a systematic and transparent approach to the investigation and understanding of the potentially modifiable barriers and enablers to behaviours that influence vitamin D-related behaviours. The COM-B framework explains how the interaction between one's capability (C), opportunity (O) and motivation (M) can produce or change behaviour (B), thus outlining all potential influences on the targeted behaviour (Michie et al. 2011).
2.3 Setting and participant selection
The study was conducted in a general practice in London where the first author worked as a Nurse Practitioner. The practice is in a deprived area of England and is very ethnically diverse. Internal practice data shows that of a practice population of around 2000 patients, the largest single ethnicity is people of Bengali origin at 35%. The data regarding speaking English is limited, however practice appointment data shows the highest proportion of appointments over the last 5 years are for women of Bengali origin. The study sample was drawn from patients registered with the Practice.
2.3.1 Inclusion criteria
A convenience sampling approach was adopted aiming for 15-20 participants providing a balance between pragmatic considerations, including the time available to complete the study, the availability of the Bengali interpreter, and the aim to obtain a representative sample within the study population.
2.4 Data collection
Potential participants were sent a letter inviting them to take part in the study, written in English and Bengali and were asked to provide informed consent for participation in the study. Semi-structured telephone interviews were conducted by the first author; face-to-face interviews were not possible as COVID-19 pandemic restrictions were still in place. The Bengali interpreter facilitated the two-way translation for participants who were unable to communicate in English.
The interview guide was developed based on the COM-B behaviour change model (Michie et al. 2011) to address women's behaviour related to vitamin D supplementation. Interviews, each ranging from 30 to 45 minutes, were recorded using a digital Dictaphone and transcribed verbatim. All transcripts were de-identified and each participant was given a study identification number for reporting purposes.
2.5 Data analysis
Thematic analysis was conducted in accordance with the principles outlined by Braun and Clarke (2006). This entailed a rigorous process of data familiarization, generating initial codes, and searching for themes that describe similar underlying perspectives and experiences from respondents which reflect barriers and enablers to vitamin D intake. Data were analysed deductively using NVivo 12 software for qualitative analysis, and the generated themes were mapped onto the six COM-B components: physical capability; psychological capability; reflective motivation, automatic motivation; physical opportunity and social opportunity (Michie et al. 2011).
To minimise interpretive bias, 20% of transcripts were randomly selected and coded by the second author and cross-checked with those generated by the first author. Reliability was assessed by the concordance of themes and any conflict was resolved in discussion between the two authors.
2.6 Ethical considerations
The study was approved by the NHS Research Ethics Committee and received Health Research Authority approval (IRAS ID: 309401) in March 2022.
3. Findings
3.1 Participants
Interviews were conducted between April and July 2022 with 17 women of Bengali origin with an age range between 19 and 61 years (mean age = 37years, SD =9.9). For 4 women the interview was conducted in real-time translation by the Bengali interpreter. 13 of the women had vitamin D measured in the last12 months and 4 of them had vitamin D levels within the normal range; 3 women were being prescribed vitamin D by their Practice and taking regularly and 4 were obtaining this as an over the counter supplement.
3.2 Thematic analysis
Eleven themes across the six COM-B components were generated to describe factors (barriers and enablers) that influence behaviours associated with vitamin D supplementation (Table 1).
| COM-B | Component | Themes | Barriers | Enablers |
|---|---|---|---|---|
| Capability | Physical | Vitamin D intake | Forgetting to take tablets | Dossette box to aid medication intake |
| Psychological | Knowledge of vitamin D | Lack of knowledge | Knowledge of vitamin D health benefits | |
| Knowledge sources of vitamin D | Incorrect beliefs regarding food sources | Awareness of sun as a source | ||
| Awareness of population groups at risk | Lack of awareness that people of South Asian origin are at risk | Participant's work enables knowledge that people of South Asian origin are at risk | ||
| Opportunity | Social | Cultural Influences | Modest dressing as dictated by cultural norms | Investing in trips outside the UK for sun exposure |
| Low fish intake | High fish intake | |||
| Being born in the UK | Being born in Bangladesh and speaking Bengali | |||
| Cultural stigma of colourism | Sun exposure is socially acceptable | |||
| Named GP | Lack of support from HCPs to promote vitamin D intake | Positive influence of named GP | ||
| Physical | Vitamin D formulation | Tablets unpalatable | Ability to take tablets | |
| Availability of vitamin D | Financial | Prescriptions | ||
| Healthcare services | Blood tests for vitamin D levels with no action | Blood tests raise awareness | ||
| Motivation | Reflective | Government recommendations for vitamin D | Negative beliefs about food fortification | Fortification enables vitamin D intake |
| Consequences of vitamin D deficiency | Lack of physical effect seen | Joint pains if do not take |
Table source
3.3 Capability
3.3.1 Knowledge of vitamin D
Only one participant reported having no knowledge of vitamin D; all the other participants reported varying levels of knowledge of vitamin D and its effects. Two participants mentioned an increased risk for the Bengali population due to their behaviour of dressing modestly due to cultural reasons and not spending time outside.
‘I know that Bengali have a lot less because they stay indoors and they don't really stand out in the sun a lot.’ [P10]
The benefits of vitamin D to general health and the immune system were mentioned, with seven participants noting its effect on bone health.
‘Well, all I know about it is, is good. I think it's good for you. Yeah, yeah. Or overall your health, vitamin and its good for your bones.’ [P11]
3.3.2 Knowledge of sources of vitamin D
Fifteen participants were aware that sunlight was a source of vitamin D. Knowledge of sunlight fed into knowledge that Asian women may have lower levels of vitamin D due to the practice of not exposing their skin to the sun.
‘So I know you get it from the sun. I know Asian people have, I think, we have the less vitamin D and I think it's the lady because of the cover, because maybe, we cover skin…, I believe yeah, that's all I know.’ [P15]
There was a lack of awareness about foods that contain vitamin D, with five participants incorrectly believing it could be obtained from fruit and vegetables; others mentioned rice, curry and meat and three participants believed milk is a good source of vitamin D.
3.3.3 Awareness of population groups at risk
Knowledge that South Asians are a population group at risk for vitamin D deficiency was highlighted by four participants.
‘Oh, I know that a lot of the Asian minorities we are told that we lack vitamin D…. But to be honest, I don't take any supplements for vitamin D or anything like that.’ [P2]
Three participants who worked in healthcare had a more detailed knowledge of at-risk population groups and this appeared to influence behaviour as they all regularly took vitamin D supplements.
3.3.4 Vitamin D intake
Forgetting to take tablets was identified as a barrier to taking vitamin D supplements by five participants. This was identified as ‘being lazy’ by two participants and not seen as important by another participant:
‘But yes, I did forget, you know, but then I did take I think, I don't know why we forget vitamin D. I think no one doesn't really think it's very important.’ [P11]
One participant used a dossette box and this was an enabler for her to take regular vitamin D supplements.
3.4 Opportunity
3.4.1 Cultural influences
All participants dressed modestly as dictated by cultural norms, exposing only their hands and face to the sun when outside. One participant said that when sitting in her garden she would expose up to her elbows. Three participants identified this behaviour as a reason for vitamin D deficiency.
‘I cover up so I don't think I get much sun, isn't it that's why it's always so low for a lot of people, like so many Asians.’ [P16]
Three participants who were born in Bangladesh followed a traditional diet including three or more times a week, which is a good source of vitamin D.
The cultural stigma of colourism, whereby lighter skin is considered preferential, was identified as a reason for avoiding sun exposure by one participant.
‘I think the other thing, which might get me into trouble is, there's always that stigma attached to getting a tan and being dark.’ [P17]
Going outside for errands such as shopping and taking children to school was often cited as time spent outside. A number of participants reported struggling to spend time outside for a variety of reasons including migraines, Ramadan, housework, work and lack of time.
‘To be honest, it's more when I'm collecting my daughter, shopping. It's not like all because I want to get vitamin D. You know, having a walk to get the sun is mainly because of my duties.’ [P16]
3.4.2 Named General Practitioner (GP)
The participants were all registered at a single-handed GP practice, where the same GP has been working for thepast 30 years. He was spoken of as a positive influence, encouraging regular use of vitamin D supplements by five participants.
‘I think even [name of GP] said I need to take it for life once he said.’ [P14]
Two participants had learnt about vitamin D supplements during pregnancy, but neither were taking regular supplements at the time of the study. Three participants expressed the belief that healthcare professionals would offer prescriptions of vitamin D if you were ‘seriously low’, which undermined the message of taking regular supplements.
3.4.3. Vitamin D formulation
A barrier to taking vitamin D supplements was the size of the supplements, as one participant, who was prescribed vitamin D supplements, described.
‘Just I just think these tablets are too big…I find it so difficult to swallow these tablets and sometimes just puts me off from taking it.’ [P3]
One participant purchased her own vitamin D supplements as an oral spray formulation and took them regularly.
3.4.4 Availability of vitamin D
Five participants received vitamin D on repeat prescription. This was an enabler to taking regular vitamin D supplementation as, of the four participants who had replete vitamin D in their latest blood tests, two of these were receiving regular repeat vitamin D prescriptions.
All but one participant had previously been prescribed vitamin D at some point in the past and the majority had taken this prescription, but then stopped supplementation.
‘I finished the course so he would usually prescribe me some I would maybe go on and off it on a weekly basis. And then and then it will just drop off slowly. And I would forget about it.’ [P5]
However, two participants reported that although they could afford purchasing vitamin D, this was not the case for all women of Bengali origin where buying the supplements would be a barrier to vitamin D supplementation.
‘Well for me [it is ok to pay to for vitamin D] because I'm working and stuff but … I feel like if you're paying for prescription [it] might be an issue…’ [P15]
3.5 Motivation
3.5.1 Government recommendations for vitamin D
Overall, there was a positive response to the idea of buying foods fortified with vitamin D but four participants were unsure and two were against the idea, largely due to concerns around perceived effects on the food or the use of preservatives.
‘Probably not,….. I don't like things to be added in my food, I'd rather get it from the actual source.’ [P1]
‘Sort of like radiation isn't it?’ [P16]
Anger and a lack of institutional trust was highlighted by one participant who was adamant she would not change her behaviour regarding vitamin D supplements or take fortified food.
‘No, that's it. They should just leave it as it is, if anyone wants to get it they can just buy it no need to keep adding it to everything you know?’
3.5.2 Beliefs about the consequences of vitamin D deficiency
Joint pains and impact on bone health were the main consequences of not taking vitamin D tablets identified by five participants, all of whom were motivated to take regular supplements. An improvement in mood when taking supplements was also identified by two participants.
Beliefs identified by participants that prevented them taking vitamin D were a lack of importance regarding vitamin D, concerns about side effects and a lack of physical effect if taken.
‘… I haven't been told oh this is really bad. You're lacking vitamin D. And you know, this will happen, that will happen.’ [P15]
4. Discussion
The aim of this study was to explore knowledge and perceptions of vitamin D supplementation among women of Bengali origin living in the UK, underpinned by the COM-B framework.
Almost all participants had some knowledge of vitamin D, which was most likely related to previously diagnosed vitamin D deficiency.
Knowledge regarding vitamin D, however, did not always translate into behaviour, with only seven participants taking supplements regularly. This is consistent with other research showing low uptake of vitamin D supplements in both the UK generally and within the UK South Asian population (Webb et al 2106; Sutherland et al. 2021; OHID 2022). The UK Biobank cohort found 17% of Bangladeshis reported taking a vitamin D supplement as opposed to 26% Indians and 21% Pakistanis (Darling et al. 2021)
Little differentiation is made between first and second generation South Asians in earlier studies (Darling 2020). The current study showed that being first generation immigrant (born in Bangladesh and speaking Bengali) was positively associated with regular vitamin D supplementation, as was working in healthcare.
Barriers to taking vitamin D supplements in this study were the unpalatability of the tablets, which is consistent with previous research (Kotta et al. 2015) and ‘forgetfulness’ which, although not specific to vitamin D, has previously been reported as a barrier to medication adherence (Foley et al. 2021).
A lack of physical effect if not taking the vitamin D supplement was a barrier and this is similar to research into other medication (Al-Noumani et al. 2019).
An enabler to taking regular supplements was the patients' GP and testing for vitamin D deficiency. NICE (2022) guidelines state that asymptomatic people of higher risk for vitamin D deficiency do not need routine testing, but nevertheless this remains common practice (Woodford et al. 2018; Kotta et al. 2015).
The participants' biochemistry investigations showed that three (19 %) were deficient in vitamin D. This is lower than expected as previous studies have found that between 54% (Engel et al. 2008) and >90% of South Asians (Kift et al. 2013) living in the UK were deficient in vitamin D.
One reason the Bengali population may have a higher vitamin D levels could be their higher intake of fish as part of their traditional diet (Rahman 2015; Darling 2020), with seven of the participants in the study eating fish twice a week or more (Darling 2021).
A way in which nutrition could increase the intake of vitamin D is through the fortification or biofortification of food. This has been used to successfully raise levels of vitamin D in the USA, Canada and Finland, but is currently only mandatory in the UK in infant formula (Butriss et al. 2021; OHID 2022).
The participants were generally positive towards fortification, but less so towards biofortification. Those against fortification had strong feelings regarding its unnaturalness or perceived government interference, which aligns with previous research (Kotta et al. 2015, O'Connor et al. 2018).
It is important that any food that may be fortified is appropriate for high-risk population groups. Foods like wheat flour (Butriss et al. 2021) or pork (Neill et al. 2021) have been proposed for biofortification, but since the Bengali diet traditionally favours millet and rice flour (Leyvraz et al. 2015), this would not be beneficial for most people. Pork would also be unsuitable for anyone of Islamic faith, which includes the majority of Bangladeshis (Rahman 2014).
Participants were aware that sunlight was the main source of vitamin D and associated their skin covering with an increased risk of vitamin D deficiency. Overall, they appeared to spend limited time outside, similar to other studies (Darling 2021; Butriss et al. 2021; Kift et al. 2013). One participant identified ‘colourism’ as a reason not to spend time outside, a factor which was identified as the main barrier to being outside for Pakistani South Asians in the US (Shakir 2009).
4.1 Study strengths
This is the first study to provide an in-depth understanding of behaviours related to vitamin D supplementation in women of Bengali origin living in the UK. Adopting the COM-B theoretical framework to underpin the study provided a rigorous methodological strength with potential to replicate the study in other settings and populations.
4.2 Study limitations
A limitation of this study was the small geographical area from which the participants were recruited. The first author was a nurse practitioner in this practice which may be related with a degree of researcher-led bias to sample selection and interviewing.
Conclusion and implications for practice
Vitamin D deficiency is a worldwide problem which is especially pronounced for ethnic minorities in the UK.
The participants were knowledgeable regarding vitamin D but few were taking supplements regularly. Participants who were taking vitamin D supplementation regularly were more likely to have been born in Bangladesh, have vitamin D supplements on repeat prescription and be influenced by their GP. The Government's call for evidence (OHID 2022) to explore biofortification requires careful consideration to ensure modifications are culturally appropriate to population groups at high risk of vitamin D deficiency in the UK.