A US study has found that sufferers of Parkinson's disease had depleted levels of vitamin D in their body. It is not yet know whether the vitamin deficiency is the cause or result of having the disease.

The study which appears in the journal Archives of Neurology found that 55% of Parkinson's suffers had a depletion of vitamin D, compared with 35% of the healthy volunteers. Researcher Dr Marian Evatt said: "We found that vitamin D insufficiency may have a unique association with Parkinson's, which is intriguing and warrants further investigation."

Parkinson's disease affects nerve cells in several parts of the brain, particularly those that use the chemical messenger dopamine to control movement. Symptoms include stiffness, tremor and slowed movements.

Previous studies have shown that the part of the brain affected most by Parkinson's, the substantia nigra, has high levels of the vitamin D receptor, which suggests vitamin D may be important for normal functions of these cells.

The body's ability to produce vitamin D decreases with age, making older people more prone to deficiency.

Vitamin D plays a role in bone formation and it is needed to regulate blood pressure and insulin levels and maintain the nervous system. Studies have also linked low vitamin D levels with increasing the risk of several cancers and auto-immune diseases such as multiple sclerosis and diabetes.

Vitamin D is primarily formed in the skin by exposure to sunlight. It can also be found in foods such as oily fish and eggs.