Depression is one of the most disabling diseases. It affects approximately 5.7% of older adults. In parallel, there is a high prevalence of vitamin D deficiency in this population, and it advantages the development of depressive symptoms. There are few studies about the influence of the association of depression and vitamin D deficiency on mortality.

To investigate whether the combination of depression and vitamin D deficiency increases the mortality risk in older adults.

It is a cohort study with data from wave 6 (2012-3) of the English Longitudinal Study of Ageing, a population-based study with adults aged 50 years and over, living in England. Depression was measured by the Center for Epidemiologic Studies – Depression (CES-D-8) with a cut-off point of ≥4 symptoms, and deficiency of vitamin D (<25 nmol/L) was estimated by the blood levels of 25-hydroxyvitamin D [25(OH)D]. Thus, four groups were formed: depression/25(OH)D deficiency, no depression/no 25(OH)D deficiency, depression/without 25(OH)D deficiency, and no depression/with 25(OH)D deficiency. Follow-up time was the interval between the wave 6 interview and the last contact (wave 7 or wave 8) or death, and the maximum was 60 months. Stata 14.0 was used to perform Kaplan-Meier curves and Cox regression. The adjustments were by age group, sex, wealth, physical exercise, smoking, alcohol consumption, body mass index, basic and instrumental activities of daily living, and chronic and circulatory diseases.

Of the 5,050 participants, 22.5% had depression, and 15.1% had 25(OH)D deficiency. When combining the outcomes, 4.85% had depression/25(OH)D deficiency and 67.2% had no depression/25(OH)D deficiency. The combination depression/25(OH)D deficiency was more prevalent in women, lower wealth quintile, sedentary, smokers, obese, with difficulties in activities of daily living, and with chronic and circulatory diseases. At the end of the follow-up, the survival rate was 19.1% (95%CI:3.3–44.8) in those with depression/25(OH)D deficiency and 50.4% (95%CI:36.0–63.1) in the opposite group. In the adjusted analysis, the risk of death was 78% (95%CI:1.17–2.70) higher in the depression/25(OH)D deficiency group compared to the no depression/without 25(OH)D deficiency group. The other groups (depression/no 25(OH)D deficiency, no depression/ with 25(OH)D deficiency) had no significantly increased risk of death. Sensitivity analysis confirms the importance of grouping because depression alone is a risk factor for mortality (HR:1.33; 95%CI:1.02–1.73), while 25(OH)D deficiency alone is not (HR:1.26; 95%CI:0.95–1.68).

The grouping of depression and 25(OH)D deficiency is an independent mortality risk in older adults. The maintenance of adequate levels of 25(OH)D in this population is a challenge because there is a reduction in its metabolism in the skin and difficulty in consuming source foods. Thus, it is imperative to pay attention to the screening of depressive symptoms and 25(OH)D deficiency. Proper management of these conditions will allow for greater independence and better health for the elderly.

It is important to identify, intervene and treat individuals with vitamin D deficiency or increased depressive symptoms to reduce these risk factors and improve the survival of the elderly.