A new study by researchers from The Irish Longitudinal Study on Ageing (TILDA) at Trinity College Dublin suggests that a deficiency in vitamin D is associated with a substantial increased risk of depression over a four-year follow-up period.

It is well-recognized that later life depression can significantly reduce quality of life and is a potent risk factor for functional decline, admission to residential care and early death. Moreover, the majority of older adults are undiagnosed given the complex nature of depression.

The findings form part of the largest representative study of its kind and appear in The Journal of Post-Acute and Long-Term Care Medicine (JAMDA).

Vitamin D is essential for bone health and has recently been linked with other non-bone health outcomes such as inflammation and diabetes. Small studies have found links between vitamin D and depression but few have followed up with the same affected people over time, while others have not taken into account other factors that can also affect depression.

These findings are important as researchers discovered that 1 in 8 older Irish adults are deficient in vitamin D.

The current study investigated the links between vitamin D and depression in older Irish adults and then re-examined the participants four years later to see if vitamin D status affected the risk of developing depression.

The authors found that:

• vitamin D deficiency was associated with a 75 percent increase in the risk of developing depression by 4 years;
• this finding remained robust after controlling for a wide range of relevant factors including depressive symptoms, chronic disease burden, physical activity and cardiovascular disease;
• furthermore, excluding participants taking antidepressant medication and vitamin D supplementation from the analyses did not alter the findings.

Researchers believe the findings could be due to the potential direct effect of vitamin D on the brain. That is, given the structural and functional brain changes seen in late life depression, vitamin D may have a protective effect in attenuating these changes.

Similarly, other studies have shown that vitamin D status has also been linked with neurodegenerative conditions such as dementia, Parkinson’s disease and multiple sclerosis.

Although the benefits of vitamin D remain debatable, vitamin D status is relatively easy and inexpensive to modify through supplementation or fortification. Interestingly, in Ireland, fortification of food products with vitamin D is voluntary and few manufacturers fortify their products.

Commenting on the significance of the research, first author of the study and Specialist Registrar in Geriatric Medicine, Dr. Robert Briggs, said, “This is the largest representative and most comprehensive study of depression risk and vitamin D status in older adults ever conducted in Ireland. Our findings will provide useful information to help inform public health policy, particularly regarding the proposition of the usefulness of vitamin D treatment/supplementation for depression.”

Senior author Dr. Eamon Laird added, “This study shows that vitamin D is associated with a health condition other than bone health. What is surprising is the large effect on depression even after accounting for other control variables.

“This is highly relevant for Ireland as our previous research has shown that one in eight older adults are deficient in the summer and one in four during the winter. Moreover, only around 8 percent of older Irish adults report taking a vitamin D supplement.”

“Given that vitamin D is safe in the recommended intakes and is relatively cheap, this study adds to the growing evidence on the benefits of vitamin D for health. It also helps to continue to impress the need on our public health bodies to develop Irish vitamin D recommendations for the general public. Up to this point, these are severely lacking.”

Principal Investigator of TILDA Professor Rose Anne Kenny said, “The new finding that the development of depression could potentially be attenuated by having a higher vitamin D status could have significant policy and practice implications for Government and health services.

“It is our responsibility to now ascertain whether supplementation will influence depression. There are many reasons for vitamin D supplementation in Ireland. Benefits to something as disabling and often ‘silent’ as depression are therefore important for well-being as we age.”

Source: Trinity College Dublin