Older people who have low levels of Vitamin D may be at a higher risk of depression, a new study has found.

The new research shows that people deficient in vitamin D have high levels of parathyroid hormone, which has been linked to depression.

The researchers estimate that 13 per cent of all people over 65 are depressed.

Dutch scientists measured the blood levels of vitamin D and parathyroid hormones in 1,282 study participants between the ages of 65 and 95.

They found that 26 of them were suffering from a major depressive disorder, 169 had minor depression and 1,087 did not suffer from depression.

The study found that 38.8 per cent of men and 56.9 per cent of women had insufficient vitamin D levels.

In those people who had both major and minor depression, vitamin D levels were 14 per cent lower than in people who did not suffer from depression.

Parathyroid hormone levels were five per cent higher in those people who were minorly depressed and 33 per cent higher in those who were severely depressed, compared with those who had no depressive symptoms.

The good news, researchers say, is that low vitamin D levels in the blood and elevated parathyroid hormone levels can be easily modified through an increased intake of vitamin D and more sun exposure.

Despite the findings, researchers aren't sure whether the depression leads to the reduced vitamin D levels and elevated parathyroid hormone or vice-versa.

"Underlying causes of vitamin D deficiency such as less sun exposure as a result of decreased outdoor activity, different housing or clothing habits and decreased vitamin intake may be secondary to depression, but depression may also be the consequence of poor vitamin D status," the authors write.

They suggest more studies be undertaken to determine this relationship.

The study is published in the May issue of the journal Archives of General Psychiatry.