At the time of Census 2021, 16% of the population of England and Wales had been born outside the UK [1]. Out of this, more than a million could not speak English well or at all [2]. However, English proficiency is regarded as important for integration by both migrants and non-migrants. Migrants with better English abilities reside in less deprived neighbourhoods [3] and have more social support [4]. Migrants who speak English to their children at home are perceived by natives as being more integrated [5].

Language proficiency increases with time spent in the destination country [6, 7] - an effect largely associated with increased use of the language. Such opportunities arise during employment and conversing with others in the community [7]. There is therefore a reinforcing effect where migrants with limited or no English ability are less likely to be employed [6] and more likely to live in language enclaves [3], which in turn limit opportunities for English language use and learning. Children are more likely than adults to learn the language [7] older age is related to lower levels of English proficiency [6, 8]. Women tend to have lower proficiency in the new language compared to men [8, 9].

English proficiency is important for accessing services in the UK, such as healthcare. Research has demonstrated that even those comfortable with English can misunderstand medical terminology [10]. Despite the need for professional language services in the NHS [11, 12], interpreting services are underused, with friends, family, and/or bilingual healthcare professionals filling the gap [13]. [14] notes that healthcare professionals may attempt to act as translators even when their proficiency in the patients’ language is low. In a recent UK study, only 63% of South Asian patients with limited or no English proficiency reported using professional interpreting services in primary care [15]. Interpreter services may also be hard to access; one study found that booking interpreter-assisted appointments required additional language support [16].

Extensive literature from the USA highlights how health outcomes are worse for non-proficient speakers. Low English proficiency has been associated with lower preventative healthcare uptake, such as screenings [17], and vaccinations [18]. While disease prevalence is not necessarily higher in those with low English proficiency, evidence suggests that symptom awareness is poorer [19, 20], resulting in potential under-or misdiagnosis [20]. For non-proficient speakers with diagnosed conditions, disease awareness and management has been found to be poorer [21–26], and health interventions less effective, compared to English-proficient counterparts [27]. However, where patients receive language-concordant care, preventative healthcare uptake [17] and condition management [24, 25] are improved. As to secondary healthcare, a review by [28] concluded that non-proficient patients had fewer specialist physician visits, were more likely to forgo necessary medical care, less likely to receive preventative care, and more likely to be re-admitted into hospital within 30 days.

However, the healthcare system in the USA differs markedly from UK’s universal coverage system. Within the UK, 2011 Census data shows that only 65% of those who could not speak English well or at all had self-reported ‘good’ or ‘very good’ health - compared to 88% of those who could [29]. There is also quantitative evidence that non-English language preference is related to higher rates of chronic heart disease (CHD), but not stroke or hypertension [30], although the latter could be related to underdiagnosis [31]. Evidence on the relationship between English ability and diabetes is mixed [30, 31], as is that between English ability and obesity [30, 32]. However, these studies have focused on the South Asian population [31] and cardiometabolic disease [30–32]. Extant studies have not quantified the relationship between healthcare utilisation and language proficiency. Qualitative studies have focused on healthcare experiences. Those with limited proficiency in English report feeling discriminated due to their poor command of English [33–35]. In some cases, a limited command of English may affect migrants’ understanding of how the NHS works [36], which in turn leads to misuse of the healthcare system such as use of emergency services for non-emergency conditions [37, 38]. How limited English proficiency differentiates migrants’ health and healthcare utilisation from natives in the UK is therefore neither well-described nor well-quantified.

Lack of data on English proficiency has contributed to this evidence gap. Routine healthcare records from primary and secondary care contain some data on English proficiency but have so far been under-used. This study uses healthcare records from patients in Brent, London, an area of high ethnic and language diversity, to quantify levels of health and use of care by language proficiency. A third of residents in Brent speak a main language other than English - the second highest rate of all boroughs in England and Wales - and 7% cannot speak English well or at all [39]. The contributions of this paper are to quantify non-proficient patients’ health status and healthcare utilisation and demonstrate that routine health data can be useful in understanding the health burdens of people not proficient in English.