Are over-the-counter fish oil supplements effective and safe for treating mood disorders? Studies on the top 10 fish oil supplements available in New Zealand
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Background Due to the rapid increase in the incidence of major depression and bipolar disorder, these disorders are expected to surpass cardiovascular disease as the leading health concern worldwide over the next decade. The current front line treatment, psychotropic medications, is not having an impact on the rising incidence of mood disorders; as such alternative treatments are required. One treatment that is gaining attention as a potentially effective treatment for mood disorders is omega-3 fatty acids, found in fish oil supplements. However, there are worries about increasing environmental levels of mercury and their implications for human health. Since mercury bioaccumulates in marine species, there is particular concern about mercury levels in fish oil supplements. Methods Efficacy of omega-3 fatty acids: 22 clinical research trials assessing the efficacy of omega-3 fatty acids in the treatment of mood disorders were reviewed. In addition, the ingredients and doses of over-the-counter fish oil supplements were examined. The amounts of omega- 3 fatty acids contained per capsule were determined by an independent laboratory using Gas Chromatography on the 10 most popular over-the-counter fish oil supplements and were compared with amounts stated on product labels. These doses were then compared to the doses used in the reviewed research trials. Mercury levels: the fish oil supplements were analysed for mercury by an independent laboratory using Inductively Coupled Plasma Mass Spectrometry. Results Efficacy of omega-3 fatty acids: Results from the 22 clinical trials selected revealed that 50% of trials showed omega-3 fatty acids to be more effective than placebo in the treatment of mood disorders, and 50% of trials showed no benefit of omega-3 fatty acids over placebo. Independent laboratory tests indicated that product labels for 50% of the supplements were accurate regarding omega-3 fatty acid content, whereas 50% contained between 48 – 69% of amounts stated on labels. Product labels recommend a minimum of three and maximum of seven fish oil capsules per day for brain health. To determine the potential efficacy of these doses for managing mood disorders, four statistical analyses were performed using a two-tailed, nonparametric Mann-Whitney test. The first and second analyses compared the effective dose in the positive clinical trials to a seven capsule dose (label vs. actual amounts) from over-the-counter supplements. The difference in dose was non-significant in both analyses. The third and fourth analysis compared the effective dose in clinical trials to a three capsule dose (label vs. actual amounts) from the supplements analysed. The third statistical analysis revealed a non-significant difference between the dose used in the clinical trials and a three capsule dose based on product labels. Conversely, the fourth analysis showed a significantly greater (p = .001) dose of omega-3 fatty acids in clinical trials reviewed versus the actual amount of omega-3 fatty acids in over-the-counter fish oil supplements. Mercury levels: mercury was not detected in any sample. Conclusions These findings indicate a daily dose between three and seven capsules of the most popular New Zealand over-the-counter supplements may ameliorate mood symptoms. Importantly, the risk of mercury contamination is negligible.