**Background:** Physical inactivity is a major global health problem, increasing the risk of long-term health conditions and premature mortality. Digital health interventions show promise for promoting physical activity, but inadequate digital health literacy may limit their effectiveness. This study aimed to examine the association between digital health literacy and physical activity levels, and to test whether long-term health conditions modify this association.
**Methods:** A cross-sectional survey was sent to 34,000 randomly selected inhabitants (≥16 years) in Region Zealand, Denmark, from February 5 to May 12, 2021. A total of 19,231 participated (response rate 57%). The survey included the Nordic Physical Activity Questionnaire-short form (NPAQ-short) and the Saltin-Grimby Physical Activity Level Scale (SGPALS) to assess physical activity, and three scales from the electronic Health Literacy Questionnaire (eHLQ): scale 1 'Using technology to process health information', scale 4 'Feel safe and in control', and scale 5 'Motivated to engage with digital services'. Physical activity outcomes were: (1) moderate-to-vigorous physical activity level (dichotomized as <30 min/week vs. ≥30 min/week), (2) compliance with WHO minimum recommendations (≥150 min moderate or ≥75 min vigorous physical activity per week), and (3) self-reported active vs. inactive (SGPALS). Long-term health conditions were categorized into body systems (e.g., mental, neurological, cardiovascular) and as somatic only, mental only, or combined. Logistic regression was used to assess associations, with sample weights to account for non-response. Models were adjusted for age, sex, ethnicity, BMI, marital status, education, and work status.
**Key Results:** The mean age was 55.6 years (SD 18.2), 54% were female. Only 25% reported no long-term health condition; 35% had three or more body systems involved. Mean eHLQ scores were 2.7 (SD 0.6) for eHLQ 1 and 5, and 2.9 (SD 0.5) for eHLQ 4. The proportion with the lowest digital health literacy scores (<2.0) was highest among those with three or more body systems involved (eHLQ 1: 19.1%; eHLQ 4: 8.8%; eHLQ 5: 18.5%). Higher digital health literacy was significantly associated with being active >30 min/week at moderate-to-vigorous intensity (fully adjusted model: eHLQ 1 OR 1.24, p<0.001; eHLQ 4 OR 1.13, p=0.012; eHLQ 5 OR 1.25, p<0.001), compliance with WHO recommendations (eHLQ 1 OR 1.33, p<0.001; eHLQ 4 OR 1.08, p=0.025; eHLQ 5 OR 1.32, p<0.001), and self-reported active (eHLQ 1 OR 1.50, p<0.001; eHLQ 4 OR 1.24, p<0.001; eHLQ 5 OR 1.54, p<0.001). No significant interaction was found for the number of body systems with long-term conditions (p=0.615, p=0.176, p=0.639) or for somatic/mental health condition categories (p=0.578, p=0.541, p=0.557).
**Clinical Implications:** This large population-based study demonstrates a consistent positive association between digital health literacy and physical activity levels, independent of long-term health conditions. Individuals with multiple long-term conditions had the lowest digital health literacy and physical activity levels, and were more likely to want support to become more active. These findings suggest that digital health interventions aimed at increasing physical activity should assess and address digital health literacy, particularly among those with multiple conditions. Strategies may include tailored education, support, or offering non-digital alternatives to avoid widening health inequities. Future research should explore causal relationships and effective interventions to improve digital health literacy.