On a day-to-day basis, supplementing with 5,000 IU of vitamin D daily during winter may be enough for people who get a lot of sun. Those who get less sun might need 10,000 IU of vitamin D in winter and 5,000 IU daily in summer. The most you can take without risk of serious side effects is 10,000 IU per day. We endorse this for people with MS and 5,000 IU a day for their family members. Note that children need proportionally smaller doses.
People with MS can feel comfortable that sunlight is likely to improve their health outcomes. Research suggests strongly that high-normal vitamin D levels are required for people with MS. In many centers, this has become accepted medical practice in the treatment of MS.
For more information on sunlight, vitamin D and MS, as well as sources, please see the MS Encyclopedia.