Researchers followed nearly 78,000 Norwegian women for 20 years to see if vitamin D intake affects the risk of developing multiple sclerosis (MS), a disease that affects the nervous system. Women who ate more vitamin D-rich foods and took supplements had about 42% lower chances of developing MS compared to those who got the least vitamin D. This study is important because it suggests that vitamin D itself—not just sunlight—may help protect against MS, especially in countries where there isn’t much sun for much of the year.

The Quick Take

  • What they studied: Whether women who eat more vitamin D have a lower chance of developing multiple sclerosis (MS) later in life
  • Who participated: 78,074 pregnant women in Norway who were enrolled between 2002-2008 and followed for about 20 years until 2022
  • Key finding: Women who got the most vitamin D from food and supplements had 42% lower risk of developing MS compared to women who got the least vitamin D. This difference was statistically significant, meaning it’s unlikely to be due to chance.
  • What it means for you: Getting adequate vitamin D through diet and possibly supplements may help reduce MS risk, particularly if you live in areas with limited sunlight. However, this doesn’t mean vitamin D is a cure or guaranteed prevention—it’s one factor among many that influence MS risk.

The Research Details

This was a prospective cohort study, which means researchers followed the same group of women over time and tracked what happened to them. The women filled out detailed food questionnaires while pregnant (between 2002-2008) that asked about their vitamin D intake from foods like fish, eggs, and dairy products, as well as any supplements they took. Researchers then tracked these women for about 20 years to see who developed MS. They used medical records and the Norwegian MS Registry to identify new MS cases. This approach is strong because it captures vitamin D intake before MS develops, which helps show that vitamin D intake came first, not after the disease appeared.

This research design is valuable because it looks at vitamin D intake before women got sick, which helps establish whether vitamin D might actually help prevent MS rather than just being associated with it. The long follow-up period (20 years) gives researchers plenty of time to see who develops MS. Additionally, studying this in Norway is particularly useful because most of the year there isn’t enough sunlight for the body to make vitamin D naturally, so researchers could separate the effects of vitamin D itself from the effects of sunlight.

This study has several strengths: it’s large (78,074 women), follows people over a long time period, uses validated food questionnaires to measure vitamin D intake, and carefully tracks MS cases through official medical registries. However, the study only looked at women in Norway, so results may not apply equally to men or people in other countries. The study also relied on women’s memory and reporting of what they ate, which could have some inaccuracy.

What the Results Show

Among the 78,074 women studied, 349 developed MS during the 20-year follow-up period. Women who developed MS had a median daily vitamin D intake of 296 international units (IU), while women who didn’t develop MS had a median intake of 333 IU—a difference of about 37 IU per day. When researchers compared women in the highest vitamin D intake group to those in the lowest group, they found a 42% reduction in MS risk (the technical measure was 0.58, with a 95% confidence interval of 0.38 to 0.89). This means if a woman in the lowest vitamin D group had a certain risk of developing MS, a woman in the highest group would have less than half that risk. The trend was statistically significant (p=0.02), meaning this difference is unlikely to be due to chance alone.

When researchers looked specifically at vitamin D supplements (rather than food sources), they found that women taking 600 IU or more per day from supplements had significantly lower MS risk compared to those taking less. This suggests that supplements may be particularly important for vitamin D protection, especially in countries like Norway where food sources and sunlight are limited.

This finding supports previous research showing that vitamin D is linked to lower MS risk. However, this study adds important new information by showing that vitamin D intake itself—not just sunlight exposure—appears to be protective. Previous studies couldn’t always separate whether it was vitamin D or sunlight that mattered, but this Norwegian study was able to make that distinction because sunlight is insufficient for most of the year there.

The study only included women in Norway, so results may not apply to men or people in other countries with different sun exposure or dietary patterns. The study relied on women reporting their diet during pregnancy, which may not be perfectly accurate. Additionally, the study couldn’t prove that vitamin D directly prevents MS—only that higher intake is associated with lower risk. Other factors not measured in the study could also play a role.

The Bottom Line

Based on this research, getting adequate vitamin D through diet (fish, eggs, fortified milk) and possibly supplements may help reduce MS risk, particularly for women in areas with limited sunlight. Current recommendations suggest 600-800 IU daily for most adults, though some experts recommend higher amounts. This evidence is moderately strong (confidence level: moderate) but should be combined with other healthy lifestyle factors. Consult with your doctor about appropriate vitamin D intake for your individual situation.

This research is most relevant for women, particularly those living in northern climates with limited sunlight, those with family history of MS, or those concerned about MS risk. Men should note that this study only looked at women, so the findings may or may not apply equally to them. People with MS should discuss vitamin D with their healthcare provider, as it may be part of their overall management strategy.

MS typically develops over years or decades, so the protective effects of vitamin D would likely take months to years to become apparent. This isn’t a quick fix—it’s a long-term preventive strategy. If you start taking vitamin D supplements, you wouldn’t expect to notice immediate changes, but consistent intake over time may contribute to reduced disease risk.

Want to Apply This Research?

  • Track daily vitamin D intake in IU (international units) from both food sources and supplements. Set a daily goal of 600-800 IU and log foods like fatty fish, egg yolks, fortified milk, and any supplements taken. Monitor weekly totals to ensure consistency.
  • If your current vitamin D intake is low, gradually increase it by: adding one serving of fatty fish (salmon, mackerel) twice weekly, choosing fortified milk or plant-based alternatives, eating eggs regularly, or discussing vitamin D supplements with your doctor. Use the app to set reminders for supplement timing and track which sources you’re using.
  • Track vitamin D intake monthly and quarterly to identify patterns. If using supplements, set app reminders for consistent daily intake. Consider getting blood vitamin D levels checked annually (with doctor approval) to ensure you’re reaching adequate levels (typically 30 ng/mL or higher). Log any health changes or symptoms to discuss with your healthcare provider.

This research suggests an association between vitamin D intake and lower MS risk but does not prove that vitamin D prevents multiple sclerosis. This study was conducted in Norway and may not apply equally to all populations. Vitamin D should not be considered a substitute for medical treatment of MS or other neurological conditions. If you have MS, are at risk for MS, or are considering vitamin D supplementation, please consult with your healthcare provider before making changes to your diet or supplement routine. Individual vitamin D needs vary based on age, location, skin tone, and other factors. This information is for educational purposes only and should not replace professional medical advice.