Vitamin D RDAs Fall Far Short in Winter

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Vitamin D RDAs Fall Far Short in Winter

American study finds that in winter, people need five to 10 times more

dietary vitamin D than the U.S. RDA, depending on skin shade; study also

finds the RDAs too low throughout the year by Craig Weatherby

-------------

According to a study from the University of California, Davis, people of

all skin shades need much more vitamin D than the official

recommendations would suggest. The new study joins a fast-growing roster

of findings that suggest an urgent need to raise the RDAs for vitamin D.

UV sunrays stimulate synthesis of vitamin in the skin, but the melanin

that colors human skin blocks those rays. Accordingly, light-skinned

people make more vitamin D compared with darker-skinned people, in

response to equal amounts of sun exposure. Human bodies manufacture

vitamin D upon exposure to sunshine, but the UV sunrays in northern

regions of the U.S. are so weak during the winter months that most

people make no vitamin D at all. Key Points

- Landmark study finds the current vitamin D RDAs woefully inadequate

after taking participants diets, sun exposure, and skin shades into

account.

- Findings suggest a need to raise the RDAs five- to 10-fold, depending

on skin shade, with dark-skinned people needing the most.

- Results fit with those of several recent investigations that found the

current RDAs grossly inadequate for the vast majority of Americans.

  Accordingly, dietary supplements, fatty fish, and fortified foods

are the only way to boost vitamin D blood levels during the winter. And

because so many people lead indoor lives and wear clothes or sunscreen

during sunnier months, they dont make very much then, either. UC Davis

team finds need for much higher RDAsA UC Davis research team led by

assistant professor Laura M. Hall, Ph.D., made two findings. Both are

sobering in terms of average vitamin D intakes in America and somewhat

unsurprising to folks who follow vitamin D research:

- Light-skinned people need at least 1300 International Units (IU) per

day during the winter.

- Dark-skinned people need 2100 to 3100 IU per day during the winter and

throughout the rest of the year. The recommendation for light-skinned

people holds even if they get abundant sun exposure, so those who get

little sun exposure need even more dietary vitamin D.

Fish fit the vitamin D bill; Sockeye salmon stand out In addition to

getting vitamin D from supplements [

http://www.imakenews.com/eletra/go.cfm?z=vitalchoiceseafood%2C417786%2Cb1h3yfLG%\

2C3179839%2CbgsH8nv

], 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 [

http://www.imakenews.com/eletra/go.cfm?z=vitalchoiceseafood%2C417786%2Cb1h3yfLG%\

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..

  But the recommendation for dark-skinned people holds true even for

those who get more sun exposure than average. To put these

recommendations in perspective, the current recommended daily allowance

(RDA) from birth up to age 50 is only 200 IU. It rises to 400 IU for

people 51 or older and to 600 IU for people 71 or older. Thus, the UC

Davis teams findings suggest the need for a five- to 10-fold increase in

recommended vitamin D intakes, compared with the current RDAs. Vitamin D

deficiency is linked to increased risk of osteopenia, osteoporosis,

muscle weakness, fractures, common cancers, autoimmune diseases,

infectious diseases, and cardiovascular diseases. Most researchers

recommend blood levels ranging from 90 to 120 nmol/L (i.e., 36 to 48

ng/mL). And even these optimal levels are conservative, since healthy

blood levels of vitamin D extend above 200 nmol/L (80 ng/mL).

Conversely, most vitamin D researchers define vitamin D deficiency as a

blood level below 50 nmol/L (20 ng/mL). New study takes sun exposure

into accountThe conclusions were based on data from 72 young adults from

Davis, California, with a wide range of skin shades and sun exposure. In

a novel approach, the UC Davis team sought to assess three factors

affecting vitamin D blood levels:

- Estimated vitamin D intake from foods and supplements, using diet

surveys.

- Actual sun exposure, based on reading from UV dosimeter badges worn by

each of the participants.

- Capacity to make vitamin D from UV sunrays, based on the measured

light reflectivity of each individual participants skin. The

participants were divided into four groups based on the light

reflectivity of their skin, and were studied for about two months in

each of the four seasons. Dark-skinned people with either low or high

wintertime sun exposure were estimated to have vitamin D levels of 24

and 42 nmol/L, respectively, and these levels were estimated to increase

to between 40 and 60 nmol/L in the summer. People of European ancestry

with low and high sun exposure in the winter were predicted to have

vitamin D levels of 35 and 60 nmol/L, respectively, and these levels

were estimated to increase to between 58 and 85 nmol/L in the summer.

Again, leading vitamin D researchers recommend blood levels ranging from

90 to 120 nmol/L (i.e., 36 to 48 ng/mL), so neither light-skinned nor

dark-skinned people in the study would reach the experts recommended

levels, even during the summer despite the fact that they live in sunny

California. For more on this topic, search our newsletter archive [

http://www.imakenews.com/eletra/go.cfm?z=vitalchoiceseafood%2C417786%2Cb1h3yfLG%\

2C231301%2CbgsH8nv

] for vitamin

D. Sources

- Hall LM, Kimlin MG, Aronov PA, Hammock BD, Slusser JR, Woodhouse LR,

Stephensen CB. Vitamin D Intake Needed to Maintain Target Serum

25-Hydroxyvitamin D Concentrations in Participants with Low Sun Exposure

and Dark Skin Pigmentation Is Substantially Higher Than Current

Recommendations. J Nutr. 2010 Jan 6. [Epub ahead of print]

- Vieth R. Why the optimal requirement for Vitamin D3 is probably much

higher than what is officially recommended for adults. J Steroid Biochem

Mol Biol. 2004 May;89-90(1-5):575-9. Review.