Forty-two participants were interviewed. The demographic features of the participants are presented in Table 1. After data analysis, two main themes including a) personal factors and b) socio-economic factors emerged as the experience of the study participants regarding the reasons for using DS. The categories and sub-categories are summarized in Table 2.
Subthemes of personal factors
Personal factors with 5 subthemes including perceived benefits of DS, history of illness, physiological condition, sociodempgraphic characteristics, and lifestyle factors were identified as one of the influencing factors for the use of DS among the participants.
The subjects indicated that perceived benefits of DS may lead to increased consumption. They told that DS may increase fitness, reduce hair loss, increase the skin health and its beauty, improve the mood, reduce the body's needs to unhealthy or unsafe foods, and fill nutrient gaps in the diet. They stated:
‘I have been taking DS such as multivitamin, selenium, zinc and vitamin C for a long time… Due to the use of these supplements, my skin is very clear and nice’ (F37), ‘When I take DS, I feel that my body becomes stronger and fresher…’ (F23), ‘DS may prevent any illness or pain’ (F32), ‘… the consumption of DS has positive effects on the mood, mind, concentration, nervous and mental health, and brain function’ (F50), ‘… I was stressed and anxious… one of my colleagues said that you probably have anemia or lack of vitamin in your body and I started to take DS’ (F29), ‘To prevent carcinogenic and pathogenic effects of environmental pollution, parasites and free radicals on my body, I take multivitamins, zinc, selenium and calcium’ (F39), ‘The quality of foods is decreasing nowadays. I feel that foods cannot meet my body's nutritional needs … ; therefore, I, my children, and other relatives need to take DS’ (F27), ‘Since fruits and vegetables are contaminated with toxins, they cannot provide the necessary vitamins, fiber and minerals to human body. Therefore, it would be better to use DS (F48).
From the participants’ perspectives, one of the factors affecting the use of DS was history of some illnesses. Many participants stated that the history of illnesses such as diabetes, lactose intolerance, hyperlipidemia, muscle aches, persistent weakness, anemia, and autoimmune diseases may affect the use of DS, ‘My immune system is weak… I am often sick. Therefore, I consume multivitamins’ (F19), ‘I have constant fatigue and weakness and my muscles ache. I feel better when I take DS’ (F40), ‘I went to the doctor and he said that, due to my weak body anemia, I should take iron supplement. I decided to take iron and folic acid and other multivitamins’ (F56), ‘My parents have diabetes. I am susceptible to this disease. I avoid a lot of foods, so, I have to take DS’ (F37).
A number of participants told that some physiological conditions such as being pregnant or planning for pregnancy, breastfeeding, and using oral contraceptive might influence the use of DS: ‘I will not get pregnant. I take supplements like Pharmaton, zinc, selenium, vitamin E, and powders like Ginseng every day to get pregnant …’ (F26), ‘I use DS to have a normal and comfortable delivery… and give birth to healthier babies’ (F33), ‘I used DS during lactation…’ (F48), ‘Everyone should take vitamin supplements, especially women that use oral contraceptives’ (F48), ‘When I take oral contraceptive pills, I use DS to prevent nausea and other side effects of these pills’ (F37).
Some participants told that sociodemographic characteristics including age, employment status, educational level, household income, and urbanization had significant effects on the use of DS, ‘DS should be taken by people aged above 32 years. The intake rates for DS increase with age’ (F64), ‘Since my and my wife's income and education level are high, we consume DS regularly…’ (F48), ‘Occupation is a factor influencing the use of DS. I am an employee and do not have enough time to prepare and eat some foods (e.g. salad and vegetable). I prefer to take DS’ (F39). ‘Those who have a good job and income are more likely to consume one or more DS…’ (F47), ‘Urbanization may generate more physical and mental concerns. The use of DS is more prevalent among people who reside in urban areas’ (F48).
Some participants stated that the use of DS was associated with lifestyle characteristics such as physical activity, tobacco smoking and attempts to control the weight: ‘DS increases energy and physical strength. I think they are essential for the body, especially for people who exercise regularly’ (F32), ‘Given that I'm very obese, I cannot eat all kinds of food. I have decided to lose weight, so I take DS’ (F45), ‘Because I am a professional swimmer, I take DS regularly’ (F19), ‘People will have better weight control and fitness if they take DS in addition to exercise and proper nutrition’ (F23), ‘The use of DS may reduce appetite and lead to better weight control’ (F30(, ‘Smoking reduces the absorption of vitamins consumed through food. I take DS because I smoke’ (F26).
Subthemes of socio-economic factors
Socio-economic factors with 3 subthemes including subjective norms, the price of food, and large-scale advertisement of DS industry were identified as one of the influencing factors in the use of DS among the participants.
The majority of the participants emphasized the importance of the impact of subjective norms on the use of DS. They mentioned that they were under pressure to use DS and their spouse, mother, sister, friends, colleagues and other people around them, pharmacy staff and technicians, health providers and social media encouraged them to use DS, ‘My wife takes DS every night. She believes that a woman should always take care of her body and it would be better for you to consume DS…’ (F30(, ‘My sister and friends introduced the types of DS to me. According to their advice, I use DS to increase my energy and reduce fatigue’ (F22), ‘Employees of pharmacies highlighted the benefits of DS to persuade people to buy and consume it’ (F21), ‘The images and labels of the products of DS are so appealing and attractive for me. When I see these packages in the drugstore, instead of buying one supplement, I buy all kinds of them’ (F28), ‘A large amount of information provided by virtual sites may increase the use of DS’ (F30(, ‘Some health care providers emphasize that taking DS may prevent aging and disease’ (F21).
Some of the participants also talked about the importance of the price of foods in increasing the intake of DS. They mentioned that the price of foods was on increase and they had to use DS, ‘Everything is expensive. We can't buy some fruits, vegetables or nuts... We have to use all kinds of multivitamins and supplements’ (F29), ‘I didn’t use any DS in the past years. After increasing the price of dairy products and meat, I take supplements every day’ (F30), ‘Nutrient-rich foods are more expensive than lower-quality foods. I have to eat multivitamins, zinc, selenium, calcium and so on to meet my body's needs’ (F54).
A number of participants told that commercial considerations of the sectors involved in the production and sale of dietary supplements are the factor affecting the use of these supplements, ‘The DS industry is so lucrative that various companies are regularly producing new multivitamins and persuade people to consume them’ (F33), ‘The huge profit of pharmacies and drug stores from the sale of DS increases marketing them. This marketing may enhance the use of DS by people’ (F39), ‘Drug stores try to sell new DS to people for more profits’ (F48).