Depression is characterized as alterations in thinking, mood, or behaviours associated with distress and/or impaired function. It remains one of the most prevalent health disorders of the 21st century, placing a considerable economic and social burden on both individuals bearing the disease and society at large. While depression prevalence is inversely correlated with indicators of national health such as GDP/GDP per capita, it remains one of the most undiagnosed disorders in many developing countries, largely due to lack of data and poor healthcare infrastructure to diagnose reliably. To reduce global mental health inequity and improve the demographic and economic transition of developing countries, it is important to estimate the prevalence of depression and determine the factors related to undiagnosed depression. West Africa is particularly at greater risk, as studies have reported up to 30-80% of mentally ill individuals in this region lack the resource or access to mental health services.To this end, Nigeria in particular is important to examine, as it remains the most populous West African nation, and the fastest growing economy in Africa. Studies have found that depression prevalence information is limited in this region, due to cited factors of poor mental health education, unregulated healthcare infrastructure, tendency for patients to describe somatic symptoms, and stigma towards individuals with mental disorders by both patients and physicians. The few studies available that have examined depression have been so in groups of psychiatric clinics, student athletes, geriatric attending clinics, postpartum women, and outpatient clinics. To date, there has yet been a comprehensive assessment of depression prevalence of higher education Nigerian students.

Full text, published, peer reviewed studies in English conducted on a post-secondary Nigerian population, including medical, pharmacy, or veterinary, and that reported a prevalence level for Major Depressive Disorder or depressive symptoms, were included. Studies that examined a sub-group of the Nigerian population did not provide sufficient information for a prevalence to be calculated, or those without a prevalence estimate, were excluded. Retrieved articles were exported to Zotero and duplicates were searched by a research assistant and removed. Two reviewers independently reviewed all titles. After title review, the two reviewers were randomly provided selected abstracts. Full-text publications for data extraction were chosen if the two reviewers agreed that the publication met inclusion and exclusion criteria. A third reviewer was used to independently assess abstracts and full-text review if there were discrepancies between the two reviewers. Data extraction was conducted by both reviewers. References of included articles were scanned for potentially relevant papers, with similar procedures of those papers for inclusion and exclusion. Grey literature was not sourced.

9 of the 18 studies had a score of 1, indicating a high risk of bias. 13 of the studies had a sample size less than 500. 9 of the studies used non-random sampling, and all studies sampled participants from university campuses. Of the 6 Nigerian regions, only the northwest, south-south, southeast, and southwest were represented. Sample sizes ranged from 81 to 1482 participants, with percentage of male participants ranging from 30.2% to 66.1%. Mean age of students across the 18 studies were from 19.09 and 26.3 years. All studies recruited participants from postsecondary educational programs at a Nigerian university. 5 of the studies were directed towards general university students, while the remaining studies evaluated either medical, pharmacy, dental, or veterinary students. All of the studies recruited participants from a Nigerian accredited university. The regional locations of the study populations are as follow: 3 studies from northwest Nigeria, 5 studies from Southeast, 2 studies from south-south, 5 studies from southwest, and 2 that collected participants from more than one region. This is the first study to examine the prevalence of depression amongst post-secondary students in Nigeria. While there was variation in the estimate for the prevalence of depression due to differing measures used, our finding is that the prevalence of depression amongst post-secondary Nigerian students is high. Depression did not seem to vary significantly between the different regions, or whether an individual was married. Depression prevalence was lower in older participants, though differences were not significant. Previous meta-analyses examining depression prevalence amongst post-secondary students have reported between 30.6% and 35.7%, while for health-related specialties such as medical or pharmacy report rates between 27.2% and 40.9%, with Africa having the highest rate of depressive symptoms. Our results are comparable to other pooled estimates of depression found in West Africa. A previous 2015 study conducted in Ghana reported a depression prevalence of 39.2% amongst university students, while a 2018 global meta-analysis found a pooled depression prevalence of 24% in low-income countries.