Girls: Vitamin D Makes Muscles Strong

Healthnotes Newswire (March 26, 2009)—Vitamin D is well known for its role in building and keeping strong bones, but new research shows that it is also important for muscle strength. A recent study found that higher vitamin D levels were associated with greater muscle power in teen girls.

Vitamin D levels linked to muscle power

In the study, blood tests were used to measure vitamin D levels in 99 healthy adolescent girls between 12 and 14 years old. The girls performed simple jumping tests to assess their jump height, velocity, force, and power.

The average vitamin D level in this group of girls was below the normal range and well below the level considered to be healthy, although none of them had symptoms of vitamin D deficiency. Jump height, velocity, force, and power were all correlated with vitamin D status: the girls with the highest vitamin D levels demonstrated the greatest muscle power, generating the highest, fastest, and most forceful jumps.

Low vitamin D levels are common

Recent attention directed at vitamin D has revealed that many people have low vitamin D levels, and that this can contribute to health problems that extend beyond the bones. Severe vitamin D deficiency in adolescence can cause symptoms such as limb pain, limb and pelvic deformities, muscle spasms, seizure disorders, and muscle dysfunction.

Among the adolescent girls in the current study, 75% had low vitamin D levels. These girls did not express clear symptoms of deficiency, but results from the jumping tests suggest that reduced muscle power might be a sign that they need more vitamin D.

Making sure teens get enough D

“These data highlight the importance of vitamin D status on muscle function in adolescent girls,” commented lead study author Dr. Kate Ward, formerly of the University of Manchester in Manchester, UK. “A reduced ability to generate forceful muscle contractions could have consequences for bone health in growing adolescents, as these forces influence the formation and shaping of bones.”

In addition, reduced muscle functioning might have a negative effect on athletic performance and could inhibit willingness to participate in physical activity, which could have implications for the overall health and well-being of girls as they enter adulthood.

Vitamin D is produced in our bodies through a series of chemical reactions that begin in sunlight-exposed skin, but spending too little time outdoors, living in a northern latitude, wearing clothing that covers most of the skin, and wearing sunscreen all interfere with vitamin D production. Adolescent girls at risk for low vitamin D status can take steps to prevent deficiency:

• While most doctors recommend people use sunscreen with an SPF of 15 all or most of the time, some feel up to 20 minutes of early morning or late afternoon sun helps the body get the vitamin D it needs. However, the American Academy of Dermatology suggests that people instead rely on supplement and diet sources of vitamin D and that they protect the skin from damage and more serious skin conditions by covering up with sunscreen at all times.

• Include fish and vitamin D–fortified foods, such as cold cereals, milk, fruit juices, margarine, and nondairy milks like soy and rice milk, in your diet. Small amounts of vitamin D are also found in egg yolks, beef liver, cheese, and some mushrooms.

• Consider supplementing your daily diet with a teaspoon of vitamin D–rich cod liver oil.

• Supplement with up to 1,000 IU of vitamin D per day, especially in the winter.

(J Clin Endocrinol Metab 2009;94:559–63)

Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, VT, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.

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