BMI and type 2 diabetes: how much do ethnicity, age, and sex matter?

Early-onset type 2 diabetes refers to a diagnosis in people younger than 40 years old. It comes with several issues: earlier mortality, quicker progression to microvascular and macrovascular problems, and poorer pregnancy outcomes for women.

Young adults aged 18 to 39 with type 2 diabetes are markedly underrepresented in research. Certain ethnicities and age groups are at high risk for type 2 diabetes, with some also making up a large part of the early-onset population. Despite this, researchers have yet to examine trends in incidence.

This study does just that. The authors used several national datasets to analyse trends in age-standardised incidence of type 2 diabetes, with a focus on factors like ethnicity and sex.¹

METHODS

• Multiple data sources were used to collect information on patients with type 2 diabetes. These patients were registered with a primary care or specialist provider in England. They were diagnosed between 2009 and 2022.

• Authors examined the changes in type 2 diabetes incidence and BMI over time. They categorised the data by age groups (20 to 29, 30 to 39, 40 to 49, etc.), ethnicity (Asian, Black, White), and sex (female and male). Population estimates were made for each year from 2011 to 2024.

RESULTS

Incidence

• Incidence rose in adults aged 20 to 39 and fell in those aged 60 to 79. The rise was steeper in females in every band under 60: 3.0% per year versus 2.1% in males at 20 to 29, 3.0% versus 1.3% at 30 to 39, and 1.8% versus 0.6% at 40 to 59.

• Males had the higher incidence in all age groups except 20 to 29, where the pattern reversed.

• Across all ages, incidence was highest in South Asian and Black patients.

• Among 20 to 29 year olds, incidence rose fastest in Black individuals (4.1% per year), driven mainly by females. In 30 to 39 year olds the fastest rise was in White individuals, with no change in Asian males.

• Incidence was broadly stable across ethnicities at 40 to 59.

BMI at diagnosis

• Median BMI within 26 weeks of diagnosis was substantially higher in younger adults. In females in 2024 it was 37.4 at 20 to 29 and 36.8 at 30 to 39, compared with 34.7 at 40 to 59 and 32.1 at 60 to 79 (p < 0.005).

• BMI at diagnosis is rising roughly twice as fast in the under-40s as in older adults, at around 0.17 to 0.21 kg/m² per year versus 0.06 to 0.11 kg/m².

• White patients had the highest median BMI at diagnosis and Asian patients the lowest, in every age group (p < 0.005). The rate of increase over time did not differ significantly by ethnicity.

CONCLUSION

Taken together, these findings point to a shift in who is developing type 2 diabetes rather than a uniform rise across the population.¹ Incidence is climbing fastest in the youngest adults while falling in the over-60s.

One explanation is a cohort effect, in which underlying susceptibility combines with rising BMI and adverse lifestyle exposures to bring diagnosis forward, depleting the pool of people who would otherwise have presented later in life. The same pattern has been described in colorectal cancer.² It is also a shift that routine assessment is poorly placed to detect, since the NHS Health Check does not begin until 40.³

The BMI data add a further dimension. Younger adults were diagnosed at a much higher median BMI than older adults, with roughly double the annual rise, consistent with successive cohorts reaching diagnosis at higher levels of adiposity and at younger ages. BMI was lower in older adults but still above ethnicity-adjusted obesity thresholds⁴, and since ageing brings progressive beta-cell dysfunction, less excess adiposity is likely to be needed to trigger type 2 diabetes in later life.⁵ Ethnicity modifies this throughout. Non-White populations develop type 2 diabetes at lower BMI,⁶ so although median BMI was lowest in Asian individuals at every age, the values in younger Asian adults still sit well above an already lower threshold.

Median BMI was higher in females in every age group, which may reflect greater opportunistic testing in women presenting for other reasons, including preconception care, pregnancy and menstrual problems.⁷ The consequence is that undiagnosed diabetes is likely to be more common in men, who consult less often.⁸ The rise in White females aged 40 to 59 is harder to attribute to ascertainment, and may reflect prevention efforts reaching this group less effectively or risk carried from previous gestational diabetes.⁹

WHAT THIS MEANS FOR PRIMARY CARE

• The high BMI seen in early-onset cases is worth making note of. Diagnosis at a younger age and at a higher weight means longer exposure to hyperglycaemia and a greater lifetime complication burden.¹⁰ The authors argue this shifts the emphasis towards weight-focused management from the start, with remission considered early in the pathway.¹¹

• Prevention is the other half of the picture. Rising BMI in younger adults suggests that existing obesity prevention efforts are not reaching this group, and the authors call for interventions prioritising diet, physical activity and the socioeconomic determinants of early-onset severe obesity, alongside improved risk-based screening. The NHS Diabetes Prevention Programme has achieved reasonable uptake among younger adults through digital delivery, but wider participation is needed.¹²

• Undiagnosed diabetes is also more prevalent in younger adults, which suggests that recruitment routes built around identified prediabetes will miss a proportion of those at risk.¹³

Younger adults with clear risk markers currently fall outside routine screening, and that gap is where a meaningful share of these cases is likely to sit.

References

1. Holman N, O'Keefe J, Gregg E, et al. Trends in type 2 diabetes incidence and BMI at diagnosis by age, sex, and ethnicity, 2011-2024: a population-based analysis of the English National Diabetes Audit. Lancet Reg Health Eur. 2026. https://doi.org/10.1016/j.lanepe.2026.101764

2. Gupta S, May FP, Kupfer SS, et al. Birth cohort colorectal cancer (CRC): implications for research and practice. Clin Gastroenterol Hepatol. 2024;22:455-469.e7. https://doi.org/10.1016/j.cgh.2023.11.040

3. NHS Health Check: applying All Our Health. GOV.UK. Updated 2022. https://www.gov.uk/government/publications/nhs-health-checks-applying-all-our-health/nhs-health-checks-applying-all-our-health

4. Caleyachetty R, Barber TM, Mohammed NI, et al. Ethnicity-specific BMI cutoffs for obesity based on type 2 diabetes risk in England: a population-based cohort study. Lancet Diabetes Endocrinol. 2021;9:419-426. https://doi.org/10.1016/S2213-8587(21)00088-7