Introduction
Nutritional supplements are among the most popular health-related products. In recent decades, their consumption has increased in developed and developing countries [1]. Reasons for the popularity of these supplements include the high costs of drugs and conventional treatments, fear of the side effects of chemical drugs, being available over the counter, easy to find via social media, and a belief in their natural origin and, thus, safety [2]. Like drugs, if Nutritional supplements are not used properly at a proper dose, they can have side effects [3, 4]. The present study aims to determine the level of knowledge and attitude of people referred to private pharmacies in Rasht, Iran, regarding Nutritional supplements.

Methods
This is a descriptive-analytical study with a cross-sectional design that was conducted for 6 months from February to July 2019. The sample size was determined 1220 at a confidence level of 95% and considering an estimated error of 2.5% using the Cochran formula. The sampling was done non-randomly and using on a continuous sampling method. Based on other studies, a self-report questionnaire was designed surveying demographic information (age, gender, education level, and occupation), information related to the use/non-use of nutritional supplements, reasons for using nutritional supplements, patients’ knowledge and attitude towards nutritional supplements, other used drugs, and the underlying diseases. 
The questionnaire was validated based on the opinions of a panel of expert including nine faculty members of the faculties of Pharmacy and Medicine, Guilan University of Medical Sciences. To determine the face validity and content validity, the content validity ratio (CVR) and content validity index (CVI) were calculated. The knowledge was measured using 9 items rated on a Likert scale as “completely agree” (1 point), “do not know” (0 points), and “completely disagree” (0 points). The knowledge score ranged from 1 to 9. A score <5 indicates poor knowledge, a score of 6-7 shows moderate knowledge, and a score of 8-9 represents good knowledge. The attitude subscale was measured by 10 items. The score ranged from 0 to 40. A score <20 indicates a negative attitude, while a score >20 represents a positive attitude. To determine the reliability, parallel forms were used for the knowledge subscale and the test re-test method with a two-week interval was used for the attitude subscale. Data were analyzed in SPSS software, version 22 using ANOVA, chi-square, independent sample test, and crosstabulation technique. P<0.05 was considered statistically significant.

Results
More than half of the participants were reported that they used nutritional supplements (Table 1), where 40.37% used 1-2 supplements. Most of them prepared nutritional supplements from pharmacies and the main reasons for using these supplements were maintaining health, appropriate treatment, and providing energy.


The mean score of knowledge was significantly different based on the education level (P<0.001), where the individuals with a higher education level had higher scores. The mean score of knowledge was also significantly different based on the occupation (P<0.001), where healthcare providers had higher scores, and the self-employed individuals had the lowest score. The mean score of knowledge was significantly different based on the use of nutritional supplements (P=0.029), where the supplement users had higher scores. The mean score of knowledge was also significantly different based on the number of supplements consumed (P=0.004), where those consumed more than two supplements had higher scores. Finally, the mean score of knowledge was significantly different based on the reason for taking the supplements (P=0.039), where individuals who used the supplements for appropriate treatment and maintaining health had the highest scores, respectively.
The attitude score was significantly different based on gender (P<0.001), with women had higher scores than men. The attitude score was also significantly different based on the use of nutritional supplements (P<0.001), where the supplement users had higher scores. The attitude score was significantly different based on the number of supplements consumed (P<0.001), where those who consumed more than two supplements had higher scores. The attitude score was also significantly different based on the source of supplement supply (P<0.001), where the individuals who prepared their supplements from fitness clubs had higher scores. Finally, the attitude score was significantly different based on the reason for use (P<0.001), where the individuals who did not know the reason for supplement use had the highest scores (Table 2).





Conclusion
In this study, only 20% of the participants had good knowledge of nutritional supplements; 26% had moderate knowledge , and the rest had poor knowledge. Regarding attitude, 76% had a negative attitude towards dietary supplements. Based on the results, the knowledge of people in Rasht about nutritional supplements is low, with a mean score of 5.14 out of a 9. Additionally, their knowledge of the side effects of different dietary supplements and their possible interactions with chemical drugs was also low. However, most individuals were aware that the use of dietary supplements cannot replace the foods. They also knew that there are supplements specific to individuals such as patients with kidney problems or pregnant women. Furthermore, it was observed that there was significant negative relationship between knowledge and attitude of the participants, such that with the increase of knowledge about nutritional supplements, attitudes become more negative. Therefore, increasing public awareness about nutritional supplements can lead to their proper and rational use.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Guilan University of Medical Sciences (Code: IR.GUMS.REC.1398.048).

Funding
This research did not receive any funding from funding organizations in the public, commercial or non-profit sectors.

Authors' contributions
Conceptualization, study design and supervision: Ehsan Aboutaleb and Hamidreza Taghvaye-Masoumi; Data collection, analysis, editing & review: Ehsan Aboutaleb; Preparing the initial draft: Delaram Rostam.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank Shaghayegh Sarrafzadeh and Ideh Dadgaran for their valuable assistance and all participants for their cooperation with this research.


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