In fact, the number of Parkinson's patients with vitamin D insufficiency, 55 percent, was significantly more than patients with Alzheimer's disease (41 percent) or healthy elderly people (36 percent).
First author Marian Evatt, MD, assistant professor of neurology at Emory, said that her team compared Parkinson's patients to Alzheimer's patients in order to know if neurodegenerative diseases in general lead to vitamin D insufficiency.
Humans usually get their dose of vitamin D from exposure to sunlight or by dietary supplements; fortified foods such as milk and packaged cereals are a minor source. Only a few foods in nature contain substantial amounts of vitamin D, such as salmon and tuna.
The body's ability to produce vitamin D using UV-B radiation from the sun decreases with age, which makes elderly people suceptibel to the risk of vitamin D deficiency.
"We found that vitamin D insufficiency may have a unique association with Parkinson's, which is intriguing and warrants further investigation," said Evatt.
The researchers explained that the connection between Parkinson's and vitamin D is the result of mobility problems in Parkinson's patients, which prevents their exposure to the sun.
The connection may also be because low vitamin D levels are in some way related to the genesis or progression of the disease.
It was found that the fraction of patients with the lowest levels of vitamin D, described as vitamin D deficiency, was higher (23 percent) in the Parkinson's group than the Alzheimer's group (16 percent) or the healthy group (10 percent).
Parkinson's disease affects nerve cells in several parts of the brain, particularly those that use the chemical messenger dopamine to control movement. The most common symptoms are tremor, stiffness and slowness of movement. These can be treated with oral replacement of dopamine.
Evatt said that earlier research has 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 results are published in the latest issue of Archives of Neurology.