Predictors of early sexual initiation among a nationally representative sample of Nigerian adolescents

No other single age group sustains the negative health outcomes from their sexual behaviours as do adolescents 10 to 19 years of age [1]. Adolescents in Nigeria have high burden of sexual and reproductive health problems [2]: the age-specific fertility rate of adolescent girls was 126 per 1,000 in 2003; and a quarter of females aged 15–19 years had begun childbearing [3]. Adolescent girls contribute 55% of all clandestine abortions in the country [4]; and the national HIV sero-prevalence figure for age 15–19 years is 3.6% [5].

Early onset of sexual intercourse is associated with increased lifetime prevalence of sexual partners, thereby increasing the risk exposure to sexually transmitted diseases, including HIV/AIDS, and pregnancy. Early sexual debut also increases the risk of HPV infection, due to cervical immaturity; and thus the risk of cervical cancer increases [6]. Additionally, given the risk of pregnancy, early sexual initiators are less likely to complete their schooling thereby limiting their social and vocational futures.

Empirical research, primarily from developed countries, indicates that the timing of sexual debut among adolescents is influenced by a wide range of factors including: age, gender, poverty, family structure, educational level, pubertal timing, socio-economic status, self-efficacy, peer influences, religiosity, knowledge and perceived risk of sexually transmitted infections, parenting practices and parental supervision, community, media and health inequalities [7, 8].

Despite the high rates of early pregnancy and the associated sequelae relating to early sexual debut in sub-Saharan Africa, to date there has been very little research that has explored the determinants or predictors of the timing of sexual intercourse among adolescents. Where it does exist, as Blum and Mmari note [9], the majority of studies has focused on the relationships between premarital sexual initiation and socio-demographic variables but rarely go beyond that. The current study aims to address this research gap. Specifically, the aim of the study is to determine the predictors of age of sexual debut among a nationally representative sample of Nigerian adolescents.

Our final sample consisted of 1,195 males (57.7%) and 875 females (42.3%). A total of 1,661 (80.2%) reported never having had sexual intercourse (82.0% of males and 77.8% of females) (Table 3). For the sexually experienced individuals among our study population, the median age of sexual debut was slightly but not significantly lower for males (15 years) compared to females (16 years) (Mann-Whitney U test: p = 0.383).

Analysis of the data of the 2,070 never-married adolescents showed no gender difference with respect to sexual debut before age 16 (males 9.0%; females 9.1%; X² = 0.168 df = 2, p = 0.682). However, for older adolescents, females were statistically more likely to report sexual experience than males (13.0% vs. 9.0%; p < 0.001).

This study had examined the demographic, psychosocial and community factors associated with adolescent sexual initiation using nationally representative sample of Nigerian adolescents. While a number of studies have been reported on adolescent sexual behaviour in Nigeria, most were small-scale studies that disallow national generalisations.

Overall, 18.0% of male and 22.2% of female never-married adolescents (15–19 years) reported being sexually experienced in our study; figures that are consistent with other Nigerian studies [16‐21]. The NDHS, with its national coverage, provides a more reliable portrait of adolescent sexual behaviours than small-scale reports. Our figure for females 15 to 19 years old who were sexually active (22.2%) is much lower than the retrospective report of 20–24 year olds in the NDHS 75.4% of whom reported having had sex before the age of 20. That figure, however, failed to disaggregate the ever from never married youth. As reported by the NDHS, 56% of young people 20–24 years were married by the age of 20 years. Thus, married adolescents accounted for a large proportion of the sexually active females. Consistent with our findings, using the 2003 NDHS data and focusing on never-married females, Isiugo-Abanihe and Oyediran [22] reported that 20.9% of females aged 15–19 years had ever had sexual intercourse. With regards to males, our figure (18%) is, on the whole, comparable to that of 2003 NDHS, which reported 27.4% of males aged 20–24 years as having had sex by the age of 18 years and 12.7% of males as being married by age of 20. NDHS' figure of 7.9% for the proportion of males that had had sex by age 15 also compares well with our figure of 9.1% for the sub-group.

Based on secondary analysis of Demographic and Health Survey (DHS) data, Mensch and colleagues have reported that for West Africa the proportions of 20–24 years who had engaged in premarital sex were: 18.7% for Gabon (2000 DHS), 21.1% for Ivory Coast (1998 DHS), 22.0% for Ghana (2003 DHS), 24.7% for Benin (2001 DHS) [23]. Given the difference in age cohort and time difference between the periods when the various surveys were conducted, our findings on Nigerian female sexual engagement is comparable to that of female youth in many neighboring countries but significantly lower than the rates in many Francophone countries: Cameroon (35.2%; 2004 DHS), Burkina Faso (42.5%; 2003 DHS), Chad (62.5%; 1996–97 DHS), Mali (53.5%; 2001 DHS), and Niger (74.5%; 1998 DHS). The proportion of Nigerian adolescents engaged in sex is also lower than that found in many developed countries of Europe and North America [24, 25].

The higher prevalence of females engaged in sex in our study agrees with the observation of the United States National Academies of Science that more females compared to males report having had sex by age 18 in sub-Saharan Africa, while in Latin America and the Caribbean it is the reverse [26]. The present finding also questions the assertion by some that females consistently underreport and males over report their sexual activities. Likewise, an experimental study on data collection methods among unmarried adolescents in Kenya did not uncover evidence of female adolescent underreporting in face-to-face interviews when compared with the use of audio-assisted self-interview [27].

Our finding regarding a comparatively lower tendency of females with higher levels of religiosity to initiate sex during adolescence is consistent with reports of previous studies [28, 29]. As different from the findings for females, we did not find statistically significant relationship between religiosity and sexual behaviour among the males. This too is consistent with the research of Rostosky and colleagues who concluded, in their review of ten published works, that while religiosity delays the sexual debut of adolescent females, the results are mixed for adolescent males [30]. Halpern et al explored the relative impact of testosterone and religiosity on adolescent sexual behaviour and concluded that testosterone overrode religiosity [31].

Consistent with previous reports [32], personal attitude favouring delayed sexual debut was associated with avoiding sexual intercourse among both males and females. The theory of planned behaviour holds that attitudes constitute one of the determinants of health behaviour [33].

The use of alcohol, which was not significantly associated with sexual intercourse for females, was significantly associated with sex among males in the survival analysis model with psychosocial variables. It is important to note that the proxy used in the measurement of alcohol-related practices in this study was "alcohol use in the last four weeks prior to the study", which may or may not actually reflect the use of alcohol prior to sexual debut. However, noting that association between sexual engagement and alcohol use has been reported in numerous adolescent studies in different parts of the world including in the United States [34], the Caribbean [35], and Japan [36] whereas very little focus has so far been given to such relationship in the Nigerian environment, we considered it worthwhile to explore the relationship despite the potential weakness of our measure. Our finding in this dimension should be regarded as exploratory. The repeated observations of the association between adolescent sexual initiation and alcohol use are in agreement with Jessor's cluster of risk behaviours among adolescents [37] which, according to his problem behaviour theory [38], can be traced to a common underlying factor of unconventionality – the tendency to transgress social norms. Conventionality-unconventionality has been conceptualised as a dimension underlying and summarising an orientation towards, commitment to, and involvement in the prevailing values, standards of behaviour, and established institutions of the adult society [38]. In general, greater conventionality is associated with greater involvement in health-maintaining behaviours whereas greater unconventionality relates to less involvement in health-maintaining behaviour and greater involvement in health-risky behaviours.

Our findings also indicate that both males and females who have stronger belief in the efficacy of condoms and more positive attitudes to FP as well as males more convinced of their ability to access condoms were more likely to initiate sex during adolescence. While the association sounds logical, caution is needed since the cross-sectional nature of the study precludes deducing causality. Confidence that condoms will prevent unwanted pregnancy and STI can remove the "fear" element that may have inhibited a young person to engage in premarital sex. As the Extended Parallel Process Model [39] hypothesises and empirical studies have shown [40], the element of fear plays an important role in the decision-making about sex. Likewise, an adolescent's conviction of his ability to get condom when he needs it, particularly when convinced of its efficacy, may have a disinhibiting effect on sexual behaviour. On the other hand, it is equally possible that sexual debut precedes the condom-related attitude we measured. Sexually active adolescents may have sought more information on the sources for and effectiveness of condoms and through first-hand experience prove its efficacy and their ability to access condom. Studies have shown that improved access to condoms can lead to more condom acquisition by high-school adolescents though may not necessarily lead to increases in either sexual activity or condom use [41].

The present analyses showed significant regional difference in the proportion of sexually active males (12.1% north, 24.3% south; X²= 29.289, p < 0.001) and females (13.1% north, 28.7% south; X²= 30.286, p < 0.001) at bivariate level as well at multivariate level when only selected socio-demographic factors were included in the model (males: HR = 1.44, 95% CI = 1.07–1.9; females HR = 51.7; 95% CI = 11.22–2.40). However, region was not a significant independent factor when psychosocial and other factors were added to the model. Thus, it is likely but uncertain that factors other than geography distinguished the more conservative and largely Islamic North from the South with her more educated, more urban and largely Christian population. The difference recorded between the North and the South in the present study does not reflect per se actual differences in proportion of sexually active adolescents; rather, the differences are among those who initiate intercourse in premarital context. As the NDHS shows, the practice of adolescent marriage is far more prevalent in the North compared to the South [3]. Thus, a major difference between the regions regarding adolescent sexual engagement is the context of sexual activity: mostly intra-marital in the North and predominantly pre-marital in the South.

Among sexually experienced adolescents, our comparison of early and later sexual debutants surprisingly identified only few statistically significant factors at bivariate level. Literacy in English language and alcohol use were significant factors among males while some levels of education, religiosity and media exposure were significant factors among females. The reasons for this finding are not clear, but one possibility is that the power of the study to detect the differences between the two groups is low. The issue deserves further study.

One of the challenges to studying sexual behaviour is the question of the validity of the data due to recall and social desirability biases. By focusing on age 15–19 years, the possibility of recall bias, which has been noted to increase with age [42], is limited in our study. Limiting the analysis to the 15–19 age group also makes the picture more current in terms of associating timing of sexual debut and potential predictive factors. Our use of survival analysis made for adequate allowance for age censoring and avoids a common error in studies of age at first sex among adolescents [43].

A major limitation of our study, however, is that it is cross-sectional, which necessarily limits causal conclusions. In addition, some of the psychosocial factors may not have actually preceded sexual initiation. To address the limitation relating to the uncertainty of the temporal relationship between the independent variables, particularly the psychosocial factors, and sexual initiation, we presented two different survival analysis models. Whereas one excluded the psychosocial and other factors that may have uncertain temporal relationship, the other incorporated all the factors of interest in the study. With the difference in the factors identified between the two models, there is a need for further study about antecedents and predictors of adolescent sexual initiation among Nigerian adolescents using longitudinal approach.

Our interest in this study is the never-married adolescents, and we recognise that this category may be substantially different from that of the married adolescent with regards to several contextual as well as sexual behavioural factors. Early marrying adolescents may, for example, be more likely to have an early premarital sexual debut and lesser education and, thus, their exclusion poses a challenge in terms of external validity of the results. The result of our study may not be generalised to all adolescents in Nigeria particularly with the fairly high rate of marriage among adolescent females and the associated geographic diversity within the national context.

Nevertheless, our findings have significant implications for adolescent sexual and reproductive interventions in Nigeria since abstinence still constitutes a primary pillar in the prevention of HIV, other sexually transmitted infections and teenage unwanted pregnancy. Among other strategies, health education and behaviour change communication programmes targeting young people in Nigeria need to consider how the issues of myths, wrong information, and poor attitude to such simple but critical interventions such as condom use impact behaviour. Additionally, the role of religiosity (though only found for females) raises the question of the potential influence of the faith community in promoting adolescent sexual health.

A fifth of Nigerian adolescents initiate sexual intercourse prior to marriage. While this rate do not reach the levels found in Europe or North America, the special risks of HIV infection and unwanted pregnancy in sub-Saharan Africa make this an especially vulnerable population. There is, therefore, the need to ensure effective programmes that will reach those who are most vulnerable. To be effective such programmes must be built upon the understanding of those factors associated with an increased likelihood for early sexual debut.