No Influence of Dietary, Supplemental Minerals on MS Risk

Damian McNamara

April 08, 2019

Dietary or supplemental minerals including iron, phosphorous, or manganese neither guard against, nor promote, the risk of multiple sclerosis (MS), new research shows.

This lack of association emerged in a prospective study of almost 240,000 participants in the Nurses' Health Study I and II.

"Our findings do not suggest a protective or preventive potential of taking multivitamins because of the minerals contained in them. The focus could rather be on vitamin D — maintaining healthy levels and correcting deficiencies," first author Marianna Cortese, MD, of the Department of Nutrition at the Harvard T.H. Chan School of Public Health in Boston and the Department of Global Public Health and Primary Care at the University of Bergen in Norway, told Medscape Medical News.

"It is important to remain open when approaching a study question and realize that negative findings, although they can seem less exciting or disappointing at first, are as important as positive findings to advance the research field and guide future research efforts," she added.

The study was published online April 3, 2019, in Neurology.

Harmful or Protective?

Previous reports suggest minerals may contribute to MS activity and progression. Minerals may play a role because of their effects on cell function, enzyme activity, immunobiological effects and antioxidant activity.

Other researchers proposed a protective effect associated with higher vitamin D intake from multivitamins. At the same time, it remains unclear whether additional minerals in these supplements play a role in MS risk.

"Many people take multivitamins today and it was interesting to assess whether components in multivitamins — apart from vitamin D — could be protective or harmful," Cortese said.

To learn more, the investigators assessed intake of potassium, magnesium, calcium, phosphorus, iron, zinc, manganese, and copper among 175,431 of 238,371 Nurses' Health Study I and II participants. This group reported their diets every 4 years using the Food Frequency Questionnaire (FFQ).

On average, they took below the recommended daily allowance (RDA) for potassium; the RDA for magnesium, calcium, and iron; and above the RDA for phosphorus, manganese, zinc, and copper.

The investigators identified 479 new cases of probable or definite MS diagnosed during follow-up among the women completing the FFQ, and compared their mineral intake with others who did not develop MS.

Associations Between Mineral Intake and MS Risk

 

Daily Increase

Hazard Ratio, pooled

95% Confidence Interval

Potassium

100 mg

1.01

0.99 - 1.03

Magnesium

100 mg

1.08

0.96 - 1.22

Calcium

100 mg

0.99

0.97 - 1.02

Phosphorus

100 mg

1.01

0.97 - 1.05

Iron

1 mg

1.00

0.99 - 1.01

Zinc

1 mg

1.00

0.99 - 1.01

Manganese

1 mg

1.01

1.00 - 1.02

Copper

1 mg

1.08

0.95 - 1.22

 

In addition, Cortese and colleagues found no clear association with MS when comparing women ranking in the top versus bottom quintiles for mineral intake at baseline or cumulatively during follow-up.

The lack of associations reported in the study held during multivariate analyses adjusted for multiple factors that could influence MS risk, including ancestry, latitude of residence at age 15, BMI at age 18, pack-years of smoking, supplemental vitamin D, and total energy intake.

Link to Zinc?

They also performed a secondary analysis looking at the date of first reported MS symptoms. This approach yielded 289 people diagnosed with probable or definite MS during follow-up. Again, there were no links between their dietary mineral intake and MS risk, with the exception of zinc.

Women with higher total cumulative zinc intake had a lower MS risk compared with women in the lowest intake quintile (pooled HR, 0.52; 95% confidence interval, 0.34 - 0.80; Ptrend = .004).

However, although this finding suggests a protective effect with zinc, the researchers note "the overall inconsistent results for this mineral and especially the lack of association between the intake of zinc-only supplements contributing the highest doses suggests that zinc alone is unlikely to reduce MS risk. Other factors in diet or related to the intake of multivitamins might be driving the associations seen for some of the zinc exposures, or these may have occurred by chance."

"This study provides evidence that variations in intake of minerals within the range that is common among US women are not associated with MS risk," the researchers add.

The prospective collection of information on intake of different minerals was a strength of the study, as was adjusting for potential MS risk factors. The generalizability of the results beyond women of mainly Caucasian descent is a potential limitation.

Given the null finding, the researchers plan to turn their attention elsewhere. "We are continuing to assess risk factors for MS, but also risk factors for a more severe disease course," Cortese said.

A "Great Endeavor"

Commenting on the findings for Medscape Medical News, Lily Jung Henson, MD, chief of neurology at Piedmont Healthcare in Stockbridge, Georgia, and a fellow of the American Academy of Neurology, described the study as a "great endeavor to look at the potential impact of trace minerals on the development of MS."

A potential limitation of the research is that it relied on self-reported data.

"We are counting on subject recollection and reporting of diet, and extrapolation of that into guesstimates of the amount of the minerals ingested."

Potential environmental exposures to trace minerals also remain unknown, added Henson, who is also chief medical officer at Piedmont Henry Hospital in Stockbridge. Given the potential limitations, more evidence is needed, she said.

"The importance of looking into this further cannot be overemphasized."

The study was supported by grants from the National Multiple Sclerosis Society and the NIH. Cortese and Henson have disclosed no relevant financial relationships.

Neurology. Published online April 3, 2019. Abstract

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