Background
Recent evidence has indicated that vitamin D deficiency and insufficiency are becoming global epidemics [
1]. Studies conducted in Western countries have shown that vitamin D deficiency was present in 20% -25% of the total population [
2‐
4]. In the Middle East region, approximately 60%–65% of the population was affected [
1]. Vitamin D deficiency also has a significant presence in Saudi Arabia, even though there is plentiful sunlight throughout the year. The majority of studies that have measured vitamin D levels in Saudi Arabia have indicated a high prevalence of vitamin D deficiency among different population groups [
5‐
10]. A recent national survey showed that almost 40% of males and 60% of females in Saudi Arabia had vitamin D deficiency [
11].
Aside from the classical role of vitamin D in bone health and the regulation of calcium and bone homeostasis, several large observational studies worldwide have shown an association between vitamin D deficiency and the risk of coronary heart disease (CHD) and associated risk factors such as hypertension and diabetes [
12‐
16]. Furthermore, recent meta-analyses of observational studies also reported significant associations of vitamin D deficiency with cardiovascular disease (CVD) mortality [
17], and the increased risk of CVD [
18]. Thus, the existing literature of observational studies indicated an association between vitamin D deficiency and the risk of CHD. Nevertheless, to date only a few randomized controlled trials (RCTs) have been conducted to examine the effect of vitamin D supplementation on reducing the risk of CHD [
19‐
21]. However, these studies have failed to demonstrate any causal relationship between vitamin D status and the risk of CHD [
19‐
21]. These studies are flawed with small sample size. Moreover, Mendelian randomization study on the role of vitamin D in CHD illustrated that there is no association between vitamin D deficiency and the risk of CHD [
22]. However, this result is only generalizable in European ethnicity but not in Middle Eastern populations. While the casual relationship between vitamin D deficiency and the risk of CHD cannot be determined based on limited number of studies, yet vast literature consistently demonstrated an association between vitamin D deficiency and the risk of CHD.
Exposure to sunlight is the main source of vitamin D, and there are also a few dietary sources of vitamin D, including oily fish and egg yolks, as well as vitamin D dietary supplements [
23]. Although the biological factors that reduce serum vitamin D levels are known, the effects of cultural and lifestyle behaviors, as well as knowledge and attitudes about vitamin D, need further investigation. Relatively few studies have assessed knowledge and attitudes in relation to vitamin D worldwide [
24‐
27]. Only one study in Saudi Arabia has examined the knowledge and attitudes about vitamin D [
28]; however, the study had limitations such as it was conducted only among college students and with a small sample size and sex restriction (only eight females were involved) [
28].
Furthermore, in Saudi Arabia, we have demonstrated the association between vitamin D deficiency [25(OH)D < 20 ng/mL] and the presence of CHD among adults [OR: 6.5, 95% CI: 2.7–15,
p = < 0.001] [
29]. We have also found an association between vitamin D deficiency [25(OH)D < 20 ng/mL] and diabetes among subjects with CHD [OR: 2.9, 95% CI: 1.02–8.5,
p = 0.04] in Saudi Arabia [
30]. Taking into consideration the high rates of CHD and associated risk factors such as obesity, diabetes, hypertension, and hypercholesterolemia in Saudi Arabia [
31‐
34], as well as the high prevalence of vitamin D deficiency in the country [
6,
9], there is a need to effectively address these problems. Thus, it is essential to investigate whether knowledge and attitudes regarding vitamin D may play a role in establishing healthy/unhealthy behaviors that contribute to the difference in vitamin D status between CHD patients and subjects without CHD in Saudi Arabia. Therefore, this research aimed to (1) report the prevalence of vitamin D deficiency in subjects with and without CHD, (2) compare the levels of knowledge and attitudes about vitamin D between the two groups, (3) investigate and compare vitamin D-related behaviors in both groups, and (4) to examine the associations of vitamin D status with knowledge, attitudes, and behaviors about vitamin D. This information is expected to provide evidence for developing appropriate health promotions and educational interventions for the general population, thereby increasing knowledge and understanding about the importance of vitamin D and potentially reducing the risk of CHD in Saudi Arabia.
Discussion
The current study revealed a number of important findings. First, the cases with CHD had a higher prevalence of vitamin D deficiency compared with the controls. Second, knowledge of various aspects of vitamin D was lower among the CHD cases than the controls. Third, the cases with CHD had a better attitudes toward sun exposure compared with the controls; however, the controls had better attitudes toward vitamin D compared to the cases. Fourth, a higher proportion of the CHD cases were sufficiently exposed to sunlight during weekdays and weekends. Almost three-quarters of the subjects in both groups were only exposing their faces and hands to sunlight. Fifth, the controls had a higher intake of multivitamin supplements and a higher consumption of butter, oily fish, and liver compared with the CHD cases, while milk intake was higher among the CHD cases than the controls. Finally, after controlling for potential confounding factors, low levels of knowledge about vitamin D and the low intake of vitamin supplements were significantly associated with vitamin D deficiency.
The study findings demonstrated that vitamin D deficiency was significantly more prevalent in the CHD cases than the controls. Previous studies have reported similar results [
36,
37]. Based on these findings, the present study attempted to answer an important question, which are whether the higher prevalence of vitamin D deficiency in the CHD cases compared with the controls is due to differences in knowledge, attitudes, and vitamin D-related behaviors in both groups?. To the best of our knowledge, this is the first study that has compared the knowledge and attitudes about, and behaviors toward, vitamin D between subjects with and without CHD. It is also the first study to examine the associations between vitamin D status and knowledge, attitudes, and behaviors about vitamin D in Saudi Arabia.
The traditional knowledge, attitudes, and practice (KAP) survey theory suggests a direct linear relationship between knowledge, attitudes, and behaviors, which is, according to several studies, very simple and not true [
38]. This is because people’s behaviors have a multifactorial nature and depend on many factors such as socio-cultural and environmental factors, not just knowledge and attitudes [
38]. Thus, our study showed inconsistent findings between knowledge, attitudes, and behaviors in both groups.
The present study showed that the controls had higher levels of knowledge about vitamin D compared with the CHD cases. The total score of knowledge about vitamin D was higher in the controls than in the cases, including understanding the importance of vitamin D in disease prevention and knowledge of sources of vitamin D, such as sun exposure and certain foods. This difference in knowledge between the cases and controls may be due to the fact that the control subjects were more educated than the cases. These results are consistent with the multivariate logistic regression results that showed a significant association between low levels of knowledge about vitamin D and vitamin D deficiency in our sample after controlling for CHD. A study among older adults in Netherlands has reported similar results as the higher levels of knowledge about vitamin D was associated with higher vitamin D serum levels [
27].
Overall, the present study showed a lack of knowledge about vitamin D in both groups, but more specifically in the CHD cases. Approximately one-third of the controls and two-thirds of the cases have never heard or learned about vitamin D. In addition, of those who reported that they have heard about vitamin D, 38% of the controls and 63% of the cases reported that they did not know any of the vitamin D sources, including the role of sun exposure in production of vitamin D. Moreover, there was a confusion about dietary sources of vitamin D among those who reported diet as a source of vitamin D as only a few subjects knew some of the richest sources of dietary vitamin D, such as milk (4% of the cases and 10% of the controls) and fatty fish (11% of the cases and 25% of the controls). Evidence to date has also indicated low levels of knowledge about vitamin D among different populations. A study conducted in the UK showed that approximately one-third of the study participants had never heard about vitamin D, especially older participants [
24]. Likewise, low levels of knowledge about vitamin D have been reported in Chinese women [
25]. Similarly, a survey in the Netherlands revealed that only 38% of survey participants had heard about vitamin D [
27]. Relatively better knowledge about vitamin D has been reported in Australia. A survey conducted in Queensland showed that 69% of the participants knew about vitamin D, and almost 50% of them knew its role in protecting bone health [
26]. In Kuwait, a Gulf country, a cross-sectional survey indicated low levels of knowledge about vitamin D among the Kuwaiti population [
39].
With respect to attitudes toward vitamin D and sun exposure, almost half of the cases responded “I do not know” to whether vitamin D was important for health, compared to 80% of the controls responding “yes” to the importance of vitamin D for general health. This might be partly due to the higher level of knowledge among the control subjects. However, results showed that the CHD cases had better attitudes toward sun exposure than the controls as a large majority of the CHD cases said, “I like to expose all the time and/or sometimes to sunlight”, whereas a higher proportion of the controls said “I avoid exposure to or rarely expose myself to sunlight”. Similarly, only half of the controls and 65% of the cases were concerned about their current vitamin D status. These results indicated three important points. First, the controls had better attitudes toward vitamin D than the cases. Second, the cases had better attitudes toward sun exposure than the controls, even though they were less knowledgeable about vitamin D. Third, in general, our study sample had an unfavorable attitude toward vitamin D and sun exposure, with a lack of awareness about the importance of vitamin D and exposure to sunlight. Negative attitudes toward sun exposure have been reported among Arabic Gulf populations [
39]. Previous studies have also reported negative attitudes toward sun exposure, even among subjects who were considered knowledgeable about vitamin D [
25]. This is similar to our findings, as the current study highlighted contradictory results between knowledge about vitamin D and attitudes toward sun exposure. The control subjects had higher levels of knowledge about sun exposure as the main source of vitamin D; however, one-third of the controls had negative attitudes toward sun exposure and stated that they avoided or rarely exposed themselves to sunlight, which may suggest that being knowledgeable about vitamin D does not necessary influence attitudes toward exposure to sunlight as the major source of vitamin D. Furthermore, one possible explanation for cases having better attitudes toward sun exposure than the controls might be due to the interrelationship between attitudes and other variables, such as beliefs [
38]. This means cases might answer what they think it is correct or healthy, as the majority of patients are trying to act healthier after being affected by a disease.
Regarding vitamin D-related behaviors, findings related to exposure to sunlight in our study showed that even though a higher percentage of the CHD cases were sufficiently exposed to sunlight, a large percentage of the subjects in each group were not exposed to sunlight during weekdays (17.7% of the cases and 10.3% of the controls) and weekends (35.4% of the cases and 48.7% of the controls). Additionally, more than three-quarters of the participants in both groups only exposed their faces and hands to sunlight, which indicates that very small parts of their bodies were exposed to sunlight for a limited time during the day; hence, our results showed poor sun exposure behaviors among the study subjects, which explain why we did not find a significant association between vitamin D status, and sun exposure behavior in our study. Moreover, the reason the controls had lower levels of exposure to sunlight during weekdays might be due to the higher rate of employment among the controls compared to the CHD cases, which means the controls had longer hours of working at indoor offices and thus, less sun exposure during weekdays.
The current results also indicated limited consumption of vitamin D supplements and multivitamin supplements by the study subjects in general. Higher consumption of vitamin D supplements has been reported in different populations [
40]. The use of vitamin D supplements has a significant effect on vitamin D serum levels, especially among those who were rarely exposed to sunlight. The study results showed that the controls had a higher consumption of multivitamin supplements than the cases, which might have affected their vitamin D status. This result is consistent with the results of the multivariate logistic regression as it reported a significant association between vitamin D deficiency and the low intakes of vitamin supplements, including vitamin D supplements, calcium supplements, multivitamin supplements, and calcium supplements with vitamin D.
The consumption of foods rich in vitamin D including butter, oily fish, and liver was significantly higher in the controls than in the cases, except for milk. Overall, consumption of milk was relatively low in our sample, as 42% of the controls and a quarter of the cases reported never drinking milk on a weekly basis. The Ministry of Health in Saudi Arabia fortified fresh milk, powdered milk, and buttermilk with vitamin D in order to reduce the high burden of vitamin D deficiency [
41]. Previous studies have also reported low milk consumption in the Saudi population [
42]. Furthermore, the consumption of oily fish was low in our sample, especially among the CHD cases, even though Jeddah and Makkah are located on the coast. The poor consumption of butter, fish, and liver among the cases might be due to changes in their dietary patterns after being affected by CHD. Furthermore, results of the regression analysis did not show a significant association between vitamin D deficiency and the low consumption of food rich in vitamin D in our study sample, which may be due to the fact that only 10–20% of vitamin D in human bodies is obtained from food sources [
23].
The current study has several limitations. First, the study sample was small. However, the cases and controls were selected from three different hospitals in the two main cities in the western region of the kingdom; hence, it is expected that the results of the study are likely to be generalizable to Saudis living in the western region. Second, the current study did not investigate the reasons for avoiding sunlight and for the poor consumption of vitamin D supplements and/or foods rich in vitamin D among study subjects. Moreover, courtesy bias might be a weakness of this survey as participants may want to give answers that they believe the researcher want to hear. For example, a large number of cases (65%) answered they are concerned about their vitamin D status, even though about two-third of them never heard or learnt about vitamin D. On the other hand, there are limited studies of knowledge and attitudes about, and behaviors toward, vitamin D in Saudi Arabia and the Middle East region. The strength of this study was that no previous studies have compared knowledge and attitudes about, and behaviors toward vitamin D between subjects with and without CHD as well as examined the associations between vitamin D status and knowledge, attitudes, and behaviors about vitamin D in Saudi Arabia.
Conclusions
In conclusion, the present study showed that vitamin D deficiency was highly prevalent in subjects with CHD than in the controls. Knowledge about vitamin D was higher among the controls, and they had a higher intake of multivitamin supplements and a higher consumption of butter, oily fish, and liver, while the CHD cases had a higher intake of milk and were sufficiently exposed to sunlight during weekdays and weekends. Our findings, thus, suggest that low levels of knowledge about vitamin D and the low consumption of vitamin supplementations, including vitamin D, calcium, multivitamin, and calcium supplements with vitamin D, may have contributed to the high prevalence of vitamin D deficiency among the CHD cases. Although knowledge, attitudes, and behaviors may not be strongly associated with each other in this study, the results have provided valuable information for prevention of vitamin D deficiency, which may contribute to future interventions of CHD. Moreover, additional studies using qualitative approaches are essential to explore the underlying reasons for low knowledge about vitamin D and behaviors related to vitamin D including vitamin D supplementation that might have contributed to the high burden of vitamin D deficiency in Saudi Arabia.
Acknowledgment
The authors wish to thank Tunsi private hospital, King Abdul-Aziz University hospital academic affairs center and KAMC research center for their assistance in data collection.