New research published in Journals of Gerontology suggests that vitamin D plays a role in the development of depression and depressive symptoms among elderly individuals over the course of 4 years.
Elderly individuals are a high-risk group for vitamin D deficiency. Limited mobility makes it more difficult for older adults to get outside in the sun and aging skin impairs the production of vitamin D from the sun. Because vitamin D status is related to a variety of health conditions prevalent in elderly individuals, such as fractures, heart disease and dementia, research on this population is of special concern.
Depression is another health condition that is common among the elderly, affecting nearly 20% of this population.
While vitamin D has been continually linked to the development of depression, research among the elderly has been incomplete. For example, past research in older adults that examined a role for low vitamin D status in the development of depression has looked at only one gender or in patients with previously diagnosed and potentially confounding health conditions.
This was one of the main driving forces leading Dr. Julie Williams and her research team to conduct their recent longitudinal study on vitamin D and depression in well-functioning, healthy older adults.
For the study, they looked at data from 2,598 men and women from the Health, Aging, and Body Composition (Health ABC) Study.
The Health ABC Study is an ongoing prospective study looking at the relationship between body weight and functional limitations in older adults aged 70-79 years.
While the Health ABC Study included a variety of measurements, the researchers of the present study were only concerned with the vitamin D measurement taken at 1 year into the study and how it related to measurements of the development of depression and depressive symptoms.
When vitamin D levels were measured one year after recruitment, participants were grouped on whether they had a vitamin D level lower than 20 ng/ml, between 20 and 29.9 ng/ml, or greater than or equal to 30 ng/ml.
Depressive symptoms were determined using the Center for Epidemiologic Study Depression short form questionnaire (CES-D 10) at baseline and at 2, 3 and 4 years into the study. CES-D 10 is not a diagnostic tool but is a clinically reliable 10 question, 30 point score survey where a higher score indicates the presence and increased severity of depressive symptoms.
The presence of depression was determined using the Geriatric Depression Scale 15 question short form (GDS 15). GDS is a questionnaire used to assess whether an older adult has depression.
A participant was considered to have depression if they had a CES-D 10 score greater than or equal to 10 or if they used antidepressants at baseline. Presence of depression was also determined if they had a GDS score greater than or equal to 4 or used antidepressants at 1 year into the study.
A participant was considered to have developed depression if they didn’t have depression at baseline or 1 year into the study and had a CES-D 10 score greater than or equal to 10 or used antidepressants over 4 years of the study.
The researchers wanted to know if the vitamin D status one year into the study correlated with depression at baseline or at time of vitamin D measurement, and if vitamin D status correlated with onset of depression over 4 years of follow-up.
Their results showed:
- There was no relationship between vitamin D status and prevalence of depression at baseline or at one year.
- Over 4 years, depressive symptoms increased in all vitamin D categories with the greatest increase seen in individuals with the lowest vitamin D levels (P < 0.001).
- Those with vitamin D levels lower than 20 ng/ml had an average increase in CES-D score of 2.4 compared to 1.49 in those with levels greater than or equal to 30 ng/ml.
- Eighteen percent of those with levels greater than or equal to 30 ng/ml developed depression over four years compared to 35.8% of those with levels less than 20 ng/ml.
- After a full adjustment, those with levels greater than or equal to 30 ng/ml had the lowest risk of developing depression over four years.
The researchers concluded,
“Although we did not observe a cross-sectional association between vitamin D concentrations and depression in this cohort of well-functioning older adults, there was a significant association between vitamin D concentrations and change in CES-D scores over time, with individuals with vitamin D levels less than 20 ng/ml experiencing a greater increase in depressive symptoms than those with higher vitamin D concentrations.”
They went on to add,
“Furthermore, individuals with vitamin D levels less than 20 ng/ml were at a greater risk of developing depression over 4 years of follow-up than those with 25(OH)D greater than or equal to 30 ng/ml, independent of a wide range of potential confounders.”
The researchers were quick to point out key limitations to their study. They noted that the observational design of their study limits the ability to infer causation and means that they cannot rule out the possibility that depression causes low vitamin D.
Additionally, vitamin D levels were measured only once over the four years. Vitamin D levels measured continuously throughout the study may lead to different, more accurate results.
This research highlights that vitamin D is related to multiple factors of depression in a group at high-risk for both vitamin D deficiency and depression.
As with other prospective studies, randomized controlled trials are needed to follow-up and test if supplementation, and subsequent correction of vitamin D deficiency, may help protect against depression in elderly populations.