Simultaneous studies find low vitamin D levels in teen girls, and link higher D levels to greater strength
by Craig Weatherby

Many Americans of all ages have vitamin D blood levels that fall below those recommended for optimal health.

And an alarming proportion of the population is seriously deficient in vitamin D... with dire implications for personal health and ballooning healthcare costs.

and even just sub-optimalblood levels of vitamin D are linked to osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases.

These apparent effects of vitamin D deficiency are explained by the hormone-like vitamin's known physiological effects, which range across many body systems.

While vitamin D is created in the skin upon exposure to sunlight, large sections of the population may be vitamin D insufficient or deficient.

How much D” should you take?
John Cannell, M.D., founder of the non-profit Vitamin D Council, works closely with the world's leading vitamin D researchers.

He urges people to ensure they have adequate vitamin D levels... either via UV light exposure or through fatty fish and dietary D supplements.

Making adequate vitamin D takes 20-30 minutes per day in summer-strength sunlight, or under custom UV lamps. People with darker skin generally need more UB exposure.

Only blood tests can confirm your D status.

Here's what Dr. Cannell had to say in the July 2008 edition of the Vitamin D Council newsletter:
  • “Well children under the age of two should take 1,000 IU per day, over the age of two, 2,000 IU per day.
  • “Well adults and adolescents between 80 pounds and 130 pounds should start with 3,000 IU per day, over 130 pounds but less than 170 pounds, 4,000 IU per day and over 170 pounds, 5,000 IU per day.
  • “Two months later have your doctor order your first 25-hydroxy-vitamin D [calcidiol] blood test. Then adjust your dose so your 25(OH)D [calcidiol] level is between 50 and 70 ng/ml, summer and winter. These are conservative dosage recommendations.
Many teen girls are deficient:

Studies link lack of D to muscle weakness
According to an American study published in July 2007, just over half of all adolescents may be vitamin D deficient (Weng FL et al. 2007).

Similar 2006 results from the UK showed that almost three in four outwardly healthy teenage British girls might be vitamin D deficient (Das G et al. 2006).

This all-too-common lack has been linked to a host of health problems, and public health experts are ringing alarm bells.

Now, two simultaneously published studies suggest that having low blood levels of vitamin D may reduce the muscle power and force in adolescent girls.

Conversely, the results suggest that higher vitamin D levels make girls stronger.

Vitamin D deficiency is proven to weaken bones, largely because of its role in regulating calcium metabolism. But until now, little was known about the relationship between vitamin D levels and muscle power.

That knowledge gap has narrowed with the near-simultaneous publication of two studies: one coming from cloudy Britain and another announced from sunny Australia

Researchers from Britain's University of Manchester and Australia's University of Sydney conducted separate studies in adolescent girls, to look for any relationships between vitamin D levels and muscle power.

And the results should further prompt parents to ensure that their girls are getting ample amounts of the “sunshine-and-seafood” vitamin… for a wide variety of reasons that may include strength.

What the British study showed
A team lead by Kate Ward, Ph.D. recruited 99 adolescent girls at an inner city, multi-ethnic school in Manchester (Ward KA et al. 2008).

Blood samples showed that the average vitamin D levels were a low 21.3 nanomoles per liter (nmol/L), and ranged from an abysmally unhealthful 2.5 nmol/L to a very healthy 88.5 nmol/L.

Fish fit the vitamin D bill; Sockeye salmon stand out
Certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.

Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:

Vitamin D per 3.5 ounce serving*

Sockeye Salmon—687 IU
Albacore Tuna—544 IU
Silver Salmon—430 IU
King Salmon—236 IU
Sardines—222 IU
Sablefish—169 IU
Halibut—162 IU

*For our full test results, click here.
While none of the girls had any physical symptoms of vitamin D deficiency, the researchers report that 75 per cent of the screened population had very low vitamin D levels (i.e., below 15 nmol/L).

The girls' muscle strength and force were measured using technique called “jumping mechanography,” which tests a person's performance in a series of jumping activities.
  1. The largely-indoor lives led by Australians and other urbanized peoples.
  2. A junky, American-style diet low in fatty fish, which are the only substantial sources of vitamin D.
  3. The inadequately low levels of vitamin D in standard multivitamin supplements.
A team from the University of Sydney recruited 301 healthy adolescent girls (of Chinese ethnic background), and measured their vitamin D levels, various biomarkers of bone turnover, bone mineral content (BMC) and density and more.

Public health campaign to reverse D deficiencies
In “Action Statements” issued at its 2008 Annual Meeting, the American Public Health Association urged Congress and key federal agencies to take these steps:
  • The Food and Drug Administration (FDA) should add vitamin D to the list of nutrients that must appear in the Nutrition Facts Panel borne by foods sold in the U.S.
  • Federal food and health agencies should begin a vitamin D awareness campaign aimed at the general public, especially among populations at highest risk for vitamin D deficiency/insufficiency.
  • Congress should fund research to determine population-specific vitamin D intakes associated with reduced risk of chronic diseases and other conditions.
The then subjected them to tests for handgrip muscle strength, with striking results.

The girls with adequate vitamin D levels had significantly higher bone mass and muscle strength compared with those with low vitamin D levels.

The researchers attributed this in part to a lower rate of bone “remodeling” among girls with higher vitamin D levels.

As they wrote, “These findings suggest that adequate vitamin D status during adolescence is important for optimizing bone mass, which may lead to higher peak bone mass at maturity. Poor vitamin D status also compromises forearm muscle strength.”

The Aussies defined vitamin D deficiency as a blood level of 50 nmol/L or less, and severe deficiency as levels below 25 nmol/L... definitions that align well with those proposed by leading vitamin D researchers.

By those criteria, 57.8 percent of the girls in the study were vitamin D deficient and 31.2 percent were severely deficient.

The very high rates of deficiency among these girls may be due in part to the greater amounts of UV-blocking melanin pigment in people of East Asian descent.

Americans of African, Middle Eastern, and South Asian descent have generally higher rates of deficiency than whites of European descent, for the same reason.

  • Das G, Crocombe S, McGrath M, Berry JL, Mughal MZ. Hypovitaminosis D among healthy adolescent girls attending an inner city school. Arch Dis Child. 2006 Jul;91(7):569-72. Epub 2005 Sep 20.
  • Foo LH, Zhang Q, Zhu K, Ma G, Hu X, Greenfield H, Fraser DR. Low vitamin D status has an adverse influence on bone mass, bone turnover, and muscle strength in Chinese adolescent girls. J Nutr. 2009 May;139(5):1002-7. Epub 2009 Mar 25.
  • Outila TA, Kärkkäinen MU, Lamberg-Allardt CJ. Vitamin D status affects serum parathyroid hormone concentrations during winter in female adolescents: associations with forearm bone mineral density. Am J Clin Nutr. 2001 Aug;74(2):206-10.
  • Ward KA, Das G, Berry JL, Roberts SA, Rawer R, Adams JE, Mughal Z. Vitamin D status and muscle function in post-menarchal adolescent girls. J Clin Endocrinol Metab. 2009 Feb;94(2):559-63. Epub 2008 Nov 25.
  • Weng FL, Shults J, Leonard MB, Stallings VA, Zemel BS. Risk factors for low serum 25-hydroxyvitamin D concentrations in otherwise healthy children and adolescents. Am J Clin Nutr. 2007 Jul;86(1):150-8.