Risk of debilitating disease found reduced by moderate sun exposure and fatty fish
by Craig Weatherby
We spoke with former NASA physicist William Grant, Ph.D.—now a leading vitamin D researcher—for the first part in this series, concerning vitamin D and cancer. At the time, Dr. Grant noted that the nutrient also appears to help prevent multiple sclerosis (MS): the degenerative disease that disrupts communication between the brain and other parts of the body.
As Dr. Grant says on his Web site (www.sunarc.org), it’s been known since the early 20th century the incidence of MS increases as you go north to higher latitudes. In other words, your risk of MS grows with your distance from the equator.
Current U.S. RDAs* and safe upper limits
- Infants 0–12 months — 200 IU (5 mcg)
- Males and females 1–50 years — 200 IU (5 mcg)
- 51–70 years — 400 IU (10 mcg)
- 71 years and older — 600 IU (15 mcg)
- Pregnant women — 200 IU (5 mcg)
- Nursing women — 200 IU (5 mcg)
U.S. safe upper limits for daily vitamin D intake
- Infants 0–12 months — 1,000 IU (25 mcg)
- Males and females 1 year and older — 2,000 IU (50 mcg)
- Pregnant and nursing women — 2,000 IU (50 mcg)
* recommended daily allowances
Sunlight is the primary “source” of vitamin D—followed by rich, cold-water fish—and, as we’ll see, vitamin D helps prevent MS. This is why the increased risk of MS at higher latitudes is linked primarily to reduced sunlight exposure. Researchers estimate that if all Americans lived in southern U.S. states, the number of MS cases would drop from 400,000 to 200,000.
Note: The risk of MS also grows as consumption of saturated fat increases, and people living in northern latitudes tend to eat more of it, which is concentrated in red meats and dairy foods. However, this correlation is not as strong as the one between reduced sun exposure and increased MS risk.
What is MS?
Most researchers consider MS an autoimmune disease in which the body’s immune system attacks its own tissues: in this case, the myelin sheath that insulates nerve, causing “short circuits.” These autoimmune assaults may be triggered by unknown environmental factors, or infectious agents such as viruses.
Most people experience their first symptoms of MS between the ages of 20 and 40. Symptoms range from fairly minor to devastating, and can wax and wane mysteriously, leading to years of misdiagnosis. While MS can leave you unable to write, speak, or walk, the vast majority of patients experience moderate symptoms, including vision problems, muscle weakness in their extremities, or impaired coordination and balance.
There is no cure for MS, and many MS medications—primarily anti-inflammatory steroids such as ACTH and prednisone—have serious side effects, while some pose significant risks. Fortunately, many patients do well with no therapy.
Low vitamin D intake figures as key risk factor
A considerable body of evidence indicates that ultraviolet B (UVB) radiation from the sun—and the vitamin D it generates in the skin—are important risk-reduction factors for multiple sclerosis.
This excerpt from one recent review of the scientific literature summarizes the situation succinctly: “A number of epidemiological [population] studies have shown a protective effect of exposure to sunlight during early life and a recent longitudinal study [in which researchers observe participants over time] confirmed that vitamin D supplementation reduced life-time prevalence of MS in women.… Prevention of MS by modifying an important environmental factor (sunlight exposure and vitamin D level) offers a practical and cost-effective way to reduce the burden of the disease in the future generations.”
Researchers believe they know how vitamin D reduces the risk of MS:
- Vitamin D plays a role in helping the immune system distinguish body tissues from foreign material. In MS, the body seems to mistake its own nerve-insulating myelin sheath for foreign tissue, and tries to destroy it.
- Vitamin D regulates important aspects of the immune response—specifically, T helper cell and dendritic cell functions—in ways that decrease the intensity of the autoimmune response and the severity of symptoms.
- In addition to being a natural “immuno-regulator,” vitamin D exerts anti-inflammatory effects. (Uncontrolled, tissue-damaging inflammation is a hallmark of autoimmune disorders like MS and rheumatoid arthritis.)
The RDAs for vitamin D: too low for too long
Almost all vitamin D researchers believe that optimal vitamin D intake for adults lies in the range of 1,000 to 2,000 IU per day. Yet, the U.S. recommended daily allowance (RDA) for adults ranges from 200 to 600 IU, depending on age and maternal status (see “Current RDAs and safe upper limits,” to the right). Many expect the U.S. Institute of Medicine to raise the RDAs in the near future: a change that can’t come too soon for enhanced prevention of cancer, osteoporosis, and MS.
One way you can increase your vitamin D intake is through moderate sun exposure, in the range of 20 to 30 minutes per day. As noted in our article on vitamin D and cancer-prevention, most experts believe that the power of the vitamin D generated by sun exposure to help prevent many common cancers far outstrips the increased risk of skin cancer (See “The Neglected Nutrient, Part 1: Vitamin D vs. Cancer”).
Another way to boost your body level of vitamin D is to enjoy ample amounts of rich, cold-water fish, such as salmon, low-mercury tuna, halibut, sablefish, and sardines.