1. Introduction
In the last decades, health-related quality of life (HRQoL) has become an important issue in research. HRQol can be defined as “how well a person functions in their life and his or her perceived wellbeing in physical, mental, and social domains of health” [
1]. Still, there is a growing interest in clarifying this term as well as in identifying the factors that affect HRQoL, in order to design more effective and efficient treatments for any chronic disease [
2,
3].
Celiac disease (CD) is a common systemic disease, mediated by immune function, which manifests as an enteropathy of the small intestine, from exposure to gluten [
4] present in wheat, barley, rye, and some types of oats [
5]. Its prevalence in Europe is 1% in both children and adults [
6]. However, the variety of related clinical symptoms which may appear makes it difficult to diagnose and it is estimated that an under diagnosis of 1:7 may exist [
7]. Prevalence studies indicate a 2:1 female:male ratio [
8]. In Spain, epidemiological studies are scarce and with small samples sizes, with percentages ranging from 0.23% to 0.85% [
9,
10,
11,
12,
13,
14]. More recently, we have found a prevalence of 0.35% in Aragon [
15]. CD is considered a systemic disease that, if left untreated, can lead to a wide range of gastrointestinal and nutritional problems such as osteoporosis, infertility, or some types of lymphoma [
8]. Currently, the only treatment identified for the disease is a strict lifelong gluten-free diet (GFD).
Despite the benefits of this GFD, adherence to it is far from perfect. Different studies place this adherence in a wide range (36–90%, with a median of 70%) [
16], depending on how we define “strict adherence” and the type of measures considered. In Spain, studies have found adherence rates to be between 72% and 83% [
17,
18,
19]. This adherence to the GFD is fundamental since 30% of the cases where no improvement in CD is seen, seem to be related to continuous exposure to gluten in the diet [
20,
21]. The persistence of symptoms, despite a GFD, leads to a reduce HRQoL, especially in the emotional sphere [
22].
Several factors may play an important role in adherence to GFD, such as the cost of specific products, concern about the risk of intentional or accidental exposure to gluten, knowledge of what a GFD is, the ability to follow the diet when traveling, eating out, and at social events, belonging to a patient association, being comfortable with the GFD at work, belief in its importance to health, or changes in mood or stress [
23]. Other studies have shown the importance of self-efficacy beliefs, when measured in a specific way in the adherence to the GFD [
24,
25,
26,
27]. Within social cognitive theory, self-efficacy is defined as beliefs in one’s capabilities to organize and execute the action required to achieve given goals [
28]. It is in this context where we study self-efficacy expectations: the belief in patients with CD in organize and execute the actions required to adhere to their GFD in different situations.
Different qualitative studies [
29,
30,
31] have investigated the difficulties that people diagnosed with CD have to face in everyday life. These studies identified that they experience problems in five areas: (1) shopping: the patient with CD has difficulties reading the labelling or dealing with possible changes in the formulations of the products they usually purchase; (2) travel problems such as finding a GFD offering in another city or managing their diet in a different language; (3) challenges at work or in their studies, such as the lack of any provision of GFD options, as well as difficulties in participating in school activities and work events; (4) eating with others at home: where they are forced to correct unsafe behavior by others or avoid appearing rude with food that others have provided; (5) eating out: identifying themselves publicly as a person with CD, requesting a gluten-free menu, having an unsafe dish removed or taking out food that they have brought from home, etc., are other difficulties that a person with CD has to face.
Consequently, emotions such as isolation, shame, fear of being contaminated by gluten or not wanting to cause discomfort are common among these patients. These feelings are sometimes the cause, and on other occasions the consequence, of the restrictions on their choices, which has the effect of producing an increased workload, or the need to be constantly alert, and a source of stress [
29,
30,
31].
Partly, because of the lack of validated and cross-culturally adapted instruments, few studies have been carried out in Spain to analyze the HRQoL of patients with CD [
32]. The perceptions of social isolation or lack of awareness of the disease by society have been reported as thoughts associated with the diagnosis of CD [
33]. Other factors identified that influence the HRQoL of patients with CD in Spain are the quality of adherence to the GFD, absence of symptoms [
18], time since diagnosis, and time on a GFD [
34].
With this research, we aim to study the adherence to the GFD and HRQoL in patients with CD in Spain. We hypothesize that patients with CD with higher self-efficacy expectations will have better adherence to GFD and, therefore, a better HRQoL.
2. Materials and Methods
The study population was composed of patients residing in Spain. The inclusion criteria were being 18 years of age or older, having a medical diagnosis of CD, and being prescribed a strict lifelong GFD. These criteria were determined by answering three self-reported questions in the affirmative.
Based on our previous research [
27], patients included in the study completed a 190 item questionnaire regarding sociodemographic data (age, gender, place of residency, education, occupational status), clinical data (previous symptoms and their intensity, age at diagnosis, time with symptoms before diagnosis, time since diagnosis), and GFD related issues (associated feelings, experiences, and perceptions), and scales regarding HRQoL, adherence to the GFD, and expectations of self-efficacy. Participants also answered questions regarding the perceived adoption of recommended behaviors and their perception of the risks associated with not following those recommendations.
The patients were recruited online through the regional patients’ associations in Spain and through associations’ social networks during September–November 2019 and invited to complete the questionnaires online using Google Forms (Google, Mountain View, CA, USA). After receiving written information about the study through the regional associations, patients signed an informed consent document. The program SPSS v21 (IBM, Armonk, NY, USA) was used to perform the statistical analysis. Absolute frequencies were used in the descriptive analysis while relative frequencies were used for the qualitative analysis. Pearson’s chi-squared was used for gender in the bivariate analyses, while for quantitative variables a t-student test was used. Age group comparisons were performed by one-way ANOVA and post hoc evaluations by Scheffe’s test. Regression analyses were carried out to study the relationship between the dependent variable, HRQoL, and the independent variables of adherence to the GFD, and the other variables. In another regression analysis, adherence to the GFD was considered as a dependent variable and the rest of the factors studied as independent variables. The statistical significance was set at p < 0.05. This study was approved by the Ethics Committee of Clinical Research of Aragon (CEICA) with number CIPI16/0311.
2.1. Adherence to the GFD
Adherence to the GFD was evaluated with the celiac dietary adherence test (CDAT) questionnaire [
35]. This questionnaire consists of 7 questions. It is easy to apply and has good psychometric properties. It has the advantage of being correlated with serological and histological variables as well as with interviews with nutritionists. The questionnaire was validated in Spain and again presented good psychometric properties [
19]. Patients have to answer on a 5-point scale. The scores are additive (7–35), with higher scores indicating lower adherence. Scores below 13 indicate excellent or very good adherence, 13–17 moderate adherence, while scores above 17 indicate fair or poor adherence [
35]. We added a separate question regarding adherence, where participants were asked to rate their adherence on a 0–10 scale, considering strict adherence to GFD scores ≥ 9.
Finally, according to the CDAT cut-off point, participants were divided into a moderate/low adherence group (group 1, with scores ≥ 13) and an excellent/good adherence group (group 2, with scores < 13). We compared differences between these two groups for the variables of the study. We also divided the participants into 3 age groups to compare differences.
2.2. General and Specific Self-Efficacy
General self-efficacy was evaluated with the Spanish adaptation of the general self-efficacy scale (GSES) [
36]. This scale is comprised of 10 items (e.g., “I can solve difficult problems if I make enough effort”) to which the patient answers on a 4-point Likert scale (1 = not at all true, 2 = hardly true, 3 = moderately true, 4 = exactly true). The scores are additive in a range of 10 to 40, with the highest scores indicating greater self-efficacy. Although the authors do not set a cut-off point, we will consider the 70% of the theoretical rank (score ≥ 31) as indicative of high general self-efficacy [
37,
38].
CD specific self-efficacy was evaluated using the celiac disease self-efficacy scale (Celiac-SE) [
39] designed to measure the degree of perceived self-efficacy in adherence to the GFD in patients aged 12 years or older, in different situations such as shopping, eating at home with others, traveling, eating out, or eating at work or school. Patients answered a 25-question questionnaire between 0 (I could definitely not do this) and 10 (I am completely certain I could do this). The questionnaire provides an average score for the whole scale and for each of the areas. Scores at 7 and above indicate high self-efficacy. Cronbach’s alpha for the total scale is 0.81.
2.3. HRQoL
The HRQoL of patients with CD was evaluated using the Spanish version of the CD Quality of life survey (CD-Qol) [
32]. This questionnaire consists of 20 questions that are answered on a 5-point Likert scale. The questions are grouped into four dimensions: limitations, dysphoria, health concerns, and inadequate treatment. The scores are additive in a range of 10 to 100. Scores of 70 or higher indicate good HRQoL.
It is important to mention that we found a discrepancy in the wording of item 8, and we communicated this issue to the authors. Since all responses were considered to be additive in this questionnaire, the correct wording of this item must be negative (“I feel that diet is not sufficient treatment for my disease”). We believe that this was the original intention, but that the word “not” was accidentally omitted in the version of the questionnaire that was published in the appendix of Dorn et al.’s 2010 validation paper. This mistake can also be found in the Spanish adaptation. This item affects the subscale “inadequate treatment”.
In order to compare HRQoL with studies of other diseases, participants responded to the Spanish version of the SF 12-item Short Form Health Survey (SF-12) [
40]. It is an adaptation of the SF-36 which generates a physical component summary (PCS) and a mental one (MCS).
2.4. Perception of Risk, Perception of Adoption of Recommended Behaviors, Time Since Diagnosis, Perceived Consequences of Abandoning the Diet, Presence of Digestive and Non-Digestive Symptoms, and Presence of Associated Diseases
Additionally, we evaluated, using two questionnaires, the perception of risks and the perceived adoption of the behaviors recommended when dealing with the GFD. These two questionnaires were developed from the content in the patients’ association guide which was elaborated by experts [
41], and previously used in our research [
27,
42]. The first questionnaire was the celiac disease risk assessment questionnaire (CDRAQ). This was an 18-item questionnaire, scored from 0 (not risky) to 10 (very risky), according to a patient´s perceived risk with respect to certain behaviors. The scores are additive, with higher scores indicating a stronger perception of risk. Examples of these items are: “I consider it to be a risk to consume processed products without a gluten free label” or “not eliminating bulk products from diet”. In the present study this questionnaire showed a Cronbach’s alpha of 0.91.
The second questionnaire was the celiac disease recommended behaviors questionnaire (CDRBQ). This second questionnaire consists of 18 questions where participants must assess if they follow the recommended behaviors, rated 0 (I do not follow this recommended behavior) to 10 (I follow this recommended behavior). An example of these items is “I wash my hands after touching something with gluten”. Scores are additive and higher scores indicate stronger perception of the correct adoption of the recommended behaviors. In this study this questionnaire showed a Cronbach’s alpha of 0.81.
Other variables studied were the time since diagnosis, the perceived consequences of abandoning the diet, the presence or not of digestive or non-digestive symptoms, and the presence of associated diseases.
2.5. Perceptions Associated with CD
We also included the celiac disease perceptions and emotions questionnaire (CDPEQ) to evaluate the frequency of some perceptions and emotions in these patients. This questionnaire was developed by this research team from the results of qualitative studies [
29,
31], and used previously in our research [
42] to explore if those feelings and perceptions are common among Spanish patients with CD. This is a 17-item questionnaire that had to be answered on a 5-point Likert scale (never, sometimes, average, many times, always). The items asked included how often the patient feels that they have an unwanted role in social events, feel rejected or feel ignored by others, and questions about the frequency with which the patient experiences feelings of anxiety or sadness related to the illness.
2.6. Socio-Demographic Variables
Several sociodemographic questions related to age, place of residence, marital status, work, or educational level were incorporated.
3. Results
A total of 818 questionnaires were collected, of which 738 were from patients with CD, 45 reported non-celiac gluten sensitivity, 14 were from minors, 7 had consent problems, and 14 were incomplete.
3.1. Description of the Sample
Of the 738 patients with CD (85.3% women), 78.2% belonged to a patient association. The age range was between 18 years and 74 years (M = 39.41; SD = 11.57). Most participants had several years of experience with the disease (M = 9.80; SD = 10.12).
Table 1 below displays the main characteristics of the sample.
3.2. Adherence to GFD
In all 96.88% of the participants reported a strict adherence to GFD when asked in the separate question added to the CDAT. The CDAT results showed good adherence (M = 11.49, SD = 2.97) in
Table 2. In addition, 68.7% showed good or excellent adherence, with scores below 13 while 4.6% reported poor adherence with scores above 17. We found better adherence in those above 35 years of age (
p < 0.001). Gender differences were found with women showing greater adherence (
p = 0.012).
3.3. Self-Efficacy
Participants showed high general self-efficacy (M = 31.34; SD = 4.84) and we found differences between the high and moderate/low self-efficacy groups (p < 0.001). In relation to specific self-efficacy, this was high (M = 8.68; SD = 1.20) and we found differences between the groups of high and moderate/low adherence, with participants with better adherence to the GFD showing higher specific self-efficacy (p < 0.001).
In a more detailed analysis (
Table 3), we found that the lowest self-efficacy occurs in the area of “traveling” (M = 7.95; SD = 1.83), while the highest self-efficacy appears in the area of “eating at home with others” (M = 9.37; SD = 1.47). Here, we have also found differences between the excellent/good and moderate/low adherence groups (
p < 0.01) for each of the areas. No gender differences were found for specific self-efficacy. We found significant differences between groups (
p < 0.001). The self-efficacy levels in the 18–35 group were significantly lower (
p < 0.001) than for the 36–50 group. No differences were found between 36–50 and the >50 groups (
p = 0.069).
If we set a cut-off point of seven where lower scores indicate low/moderate self-efficacy, 9.7% have low/moderate specific self-efficacy for managing a GFD. In an area analysis, 25.9% show low/moderate specific self-efficacy for “traveling”, 15.5% for “eating at work or school”, 11.4% for “eating out”, 8.4% for “shopping”, and 7.3% for “eating at home with others”.
3.4. HRQoL
The results in HRQoL with the SF12v2 questionnaire were moderately high (M = 36.59; SD = 4.47) with the physical component (M = 16.29; SD = 2.02) being slightly lower than the mental one (M = 20.30; SD = 3.06) (
Table 4). If we move it to a scale of 0 (worst HRQoL) to 100 (best HRQoL) we get a 62.65 (physical), 67.67 (mental) and 65.34 for the overall scale. We find differences in the adherence groups for MCS (
p < 0.001) but not for the PCS. No gender differences were found in any of the dimensions.
The results relating to HRQoL measured with CDQol were high (M = 72.73; SD = 16.83). If we express the four dimensions on a scale of 0–100, “health concerns” with a 66.92% (M = 16.73; SD = 5.16) had the lowest perceived HRQoL, followed by “limitations” with 70% (M = 31.50; SD = 9.10), “inadequate treatment” with 72.70 (M = 7.27; SD = 2.28), and “dysphoria” with 86.15% (M = 17.23; SD = 3.16). Additionally, 38.8% of patients obtained a score below 70, the cut-off point above which the score indicates good HRQoL.
Significant differences in HRQol in CDQoL were found between the high and moderate/low adherence groups (p < 0.001), with higher scores for those who had better adherence to the GFD. No gender differences were found. It is the over 50 age group which shows a better HRQoL, with significant differences with the other two groups (p < 0.001), while the 18–35 group does not reach the cut-off point of 70, indicative of high HRQoL.
3.5. Perception of Risk (CDRAQ), Perception of Adoption of Recommended Behaviors (CDRBQ), Age at Diagnosis, Time Since Diagnosis, Intensity of Symptoms, and Consequences of Abandoning
The excellent/good adherence group had a higher risk perception (
p < 0.038) and reported a higher follow-up of recommended behaviors (
p < 0.001) (
Table 5). Differences between high and low/moderate adherence groups were found (
p < 0.047) for consequences of abandoning the GFD. Paradoxically, the low adherence group perceived the consequences of abandoning the diet to be more serious. Furthermore, differences in symptom intensity after transgression were found to be higher in the moderate/low adherence group (
p = 0.006). Age at diagnosis (
p = 0.299) and time since diagnosis (
p = 0.056) do not seem to play a major role in adherence to the GFD.
3.6. Relationship between the Variables, GFD and HRQoL
Table 6 shows the results of the linear regression to study the impact of changes in the independent variables on adherence to the GFD. After studying the main variables, we only show those that have a very clear effect: specific self-efficacy, perceived adoption of patient association recommendations, risk perception, HRQoL (when measured with CDQoL), and gender, which are all significant. The model with these five variables explains 25.9% of the variance in GFD adherence. In relation to the semi-partial correlations, the specific self-efficacy represents 6.7%, while the HRQoL represents 5.1%. This would mean that the higher the specific self-efficacy, HRQoL, and the perception of adherence, the higher the adherence to a GFD, as the perception of risks does not appear to have an effect on the adherence to a GFD. Being a woman is also a predictor of adherence.
Age, age at diagnosis, time since diagnosis, intensity of symptoms, risk perception, or belief in the serious consequences of abandonment were not predictive of adherence.
If we analyze HRQoL as a dependent variable (
Table 7), this is explained by specific self-efficacy, adherence to the GFD, time since diagnosis, age and risk perception, with the perceived adoption of the recommended behaviors not being significant. In this model, these variables explain 30.6% of the HRQoL score. As far as semi-partial correlations are concerned, the specific self-efficacy variable explains 6.2% of the variability in HRQoL, 5.5% the time since diagnosis, while adherence to the GFD, explains 4% of the variability, while risk and age, although significant, have a negligible influence, 2.6% and 1.5%, respectively. No differences based on gender are found, neither for the questionnaire as a whole nor for each of the scales.
3.7. Perceptions and Emotions Associated with Having CD, According to CDPEQ
Lastly, participants were also asked about their perceptions and emotions associated with having CD (
Table 8). The most common perceptions were of a limited gluten-free offering (68.6%), the feeling of having to be constantly alert (60.7%), or an excessive protagonism in social events (55.9%). Also noteworthy is the perception that they have to work twice as hard because of their illness (shopping, cooking, etc.). It is also common to have the feeling that they are forgotten about at social events (31.2%). With regard to the most frequent negative emotions, anger (25.2%), envy (21.4), sadness (17.2%), anxiety (14.2%), or fear (13.9%) stand out, but it is worth noting the high frequency of positive feelings associated with the disease such as pride and self-confidence (50.5%), or joy (30.9%).