Parkinson diseasePatient friendly summary

  • Sunlight appears to reduce the risk of Parkinson’s disease.
  • Vitamin D may reduce the risk of Parkinson’s disease; however, more studies are required to confirm this.

Parkinson’s disease (PD) is a chronic progressive neurological disease. It is linked to decreased production of dopamine, a nerve transmitter. PD is marked by tremor of resting muscles, rigidity, slowness of movement, impaired balance, and shuffling gait. PD also impairs speech and other bodily functions.

Approximately 500,000 people in the United States suffer from Parkinson’s, and 50,000 new cases are diagnosed each year.

Risk factors

There are a number of risk-modifying factors for Parkinson’s disease:

  • Chemicals in the environment: Chemicals, such as pesticides, are associated with PD.
  • Low uric acid levels in the blood: Uric acid acts as an antioxidant in the brain, where it could affect risk of PD.
  • Red meat consumption: This food increases uric acids, which could reduce risk of PD.
  • Milk consumption: Milk, especially milk protein (casein), increases the risk of PD. (Several studies have found lower uric acid levels associated with milk consumption.)

Sunlight exposure and PD risk

Solar ultraviolet-B (UVB) light from the sun is the most important source of vitamin D for many people. Thus, studies of sunlight exposure can indicate whether vitamin D reduces the risk of PD:

  • A study in Denmark found that outdoor work and more time spent outdoors were associated with reduced risk of PD.
  • In the United States, there is increased prevalence of PD at higher latitudes. There is less solar UVB in areas farther from the equator.

Vitamin D and Parkinson’s disease

Vitamin D levels

Two studies of vitamin D and PD indicate that:

  • In southeastern United States, people with PD have lower vitamin D blood levels than those without PD.
  • In Finland, higher vitamin D levels  were associated with reduced the risk of developing PD by two-thirds. This result was noted at a 29-year follow-up. However, the usefulness of a single blood measurement loses predictive value as time increases.

How vitamin D works

The mechanisms of how vitamin D lowers the risk of PD are not well understood. All cells in the body, including those in the brain, have vitamin D receptors (VDRs). VDRs are activated by calcitriol, the active form of vitamin D. When activated, VDRs control the expression of many genes or how genetic material is used.

Vitamin D may also reduce inflammation in the brain.


There are no reported studies using vitamin D to reduce the risk of PD. The effects of vitamin D may occur over the course of many years. This would make it difficult to determine the amount of vitamin D required. However, based on results for other diseases, it appears that keeping vitamin D levels above 40 ng/mL (100 nmol/L) would be beneficial.

The rule of thumb is that vitamin D levels rise by 6–10 ng/mL (15–25 nmol/L) for each 1000 international units (IU) (25 mcg)/day of vitamin D3. Vitamin D3 is the active form of vitamin D that is produced by the skin. However, there is considerable person-to-person variability. Thus, vitamin D levels should be measured both before and three months after starting supplements.

Vitamin D and calcium

In France, a patient with PD and low vitamin D levels (13 ng/mL [33 nmol/L]) was treated with 4000 IU [100 mcg]/day vitamin D and 1000 mg/day calcium. As a result, PD symptoms were greatly reduced.


Those with PD generally have lower bone mineral density and an increased risk of falls and hip fractures. It seems advisable that those with PD seek to raise vitamin D levels to those consistent with optimal health, greater than 40 ng/mL (100 nmol/L).

Find out more…

Do you want to find out more and see the research upon which this summary is based?  Read our detailed evidence summary on Parkinson’s disease.

Page last edited: 06 May 2011