Objectives: Informal caregiving is associated with poorer mental and physical health. Little research has yet focused on objectively measured health risk factors, such as metabolic markers. The aim of this study was to investigate whether informal caregiving was associated with markers of metabolism in a large, representative UK longitudinal study. We also investigated whether more intensive caregiving, as indicated by more caregiving hours, was associated with a less favourable metabolic profile. Study design/outcome measures: Using data on 9408 participants aged 16+ from the UK Household Longitudinal Study, we explored the relationship between caregiving and metabolic markers (blood pressure, total and high density lipoprotein cholesterol, glycated haemoglobin and triglycerides). We additionally investigated the importance of caregiving intensity (number of hours spent caregiving per week). Associations between caregiving/caregiving intensity and metabolic markers were tested using gender-stratified linear regression models adjusted for age, household income, education, social class, chronic illness, number of dependent children in the household, body mass index and partnership status. Results: Men who were informal caregivers had higher total cholesterol levels than non-caregivers (3.25% higher, 95% CI: 0.07, 6.53). Women caregivers also had higher total cholesterol levels and women providing intensive care (over 20 h per week) had higher triglyceride levels (19.91% higher, 95% CI: 7.22, 34.10) and lower levels of high density lipoprotein cholesterol (8.46% lower, 95% CI: 14.51, 1.99); however, associations for women were attenuated in our final models. Conclusions: Informal caregiving is associated with less favourable lipid profiles. This may be one mechanism through which informal caregiving is associated with increased disease risk. The health of informal caregivers should be a priority for public health.