A new study from Australia found that low vitamin D levels are associated with current depression, but not past or future depression, among elderly men.
The presence of vitamin D receptors in parts of the brain that contribute to the regulation of moods has led researchers to speculate that vitamin D plays a causal role in depression.
Elderly adults are at an increased risk for vitamin D deficiency and depression compared to the general population, which has made researchers particularly interested in the role vitamin D plays in depression among elderly populations. Numerous studies have found a relationship between vitamin D status and depression. However, they have not determined whether vitamin D deficiency leads to depression or if depression leads to lower vitamin D levels.
If vitamin D deficiency causes depression, then vitamin D deficiency should be associated with future and current depression, but not necessarily past depression.
In order to provide insight on this matter, researchers recently investigated whether vitamin D levels are associated with past, current, and future depression among elderly men.
The study consisted of 3,105 men aged 71 to 88 years who donated a blood sample in the second assessment of the Health In Men Study (HIMS). HIMS is an ongoing cohort of a random community sample of 12,203 elderly men recruited between 1996 and 1998 for a study on abdominal aortic aneurysm. The participants were assessed three times: between 1996 and 1998, between 2001 and 2004, and in 2008.
The researchers used 3 strategies to identify past depression: recorded diagnoses in the Western Australian Data Linkage System (WADLS) before the date of assessment, whether they answered yes to the question ‘In the last five years, have you ever been told by a doctor that you have depression?’, or the use of an antidepressant at the time of collection of the blood sample.
Current depression was determined by using the geriatric depression scale (GDS-15). GDS-15 is a short 15-item self-report assessment used to identify depression in the elderly. A score of 7 or higher indicated depression.
In 2008, during the 6 year follow-up, participants completed a new assessment that included the patient health questionnaire (PHQ-9), a multiple choice self-report questionnaire used for screening and diagnosing mental health disorders including depression.
The researchers then compared the vitamin D levels and the presence of depression. Here is what they found:
- Men with current depression had significantly lower vitamin D levels than those with no depression or with past history of depression (p < 0.001 and p = 0.037, respectively).
- Men with vitamin D levels below 20 ng/ml were 1.65 times more likely to have current depression compared to men with vitamin D levels of 20 ng/ml or higher.
- A total of 81 out of the 2,740 men without history of depression experienced depressive symptoms during the next 6 years of follow up.
- After adjusting for potential confounding factors, men with vitamin D levels below 20 ng/ml experienced a small 3% increased incidence of depression compared to men with vitamin D levels of 20 ng/ml or higher.
The researchers summarized their findings,
“Moderate to severe vitamin D deficiency was associated with increased risk of current depression, but not past or future depression.”
The lead author, Professor Osvaldo Almeida stated,
“Our findings indicate that this association is most likely due to reverse causality, meaning that a low concentration of vitamin D is a consequence of depression because people with depression move less and are less exposed to sun light.”
The researchers acknowledged both the study’s strengths and limitations. The sample size was very large, and the assessments allowed the researchers to gather an extensive amount of information on the participants to use in adjusting for potential confounding factors.
On the other hand, vitamin D levels were only assessed once. The researchers also found that those with low vitamin D levels experienced a greater mortality rate than those with healthy levels. This takes away from the population sample considered deficient during follow-up, which results in a loss of power for the study. The results are limited to elderly men, and may not apply to women or the younger population.
Randomized controlled trials need to establish the causality between vitamin D levels and depression.