Nu­tri­tion

In win­ter, we need to go out of our way to catch enough rays to keep up vi­ta­min D pro­duc­tion.

New Zealand Listener - - CONTENTS - by Jen­nifer Bowden

In win­ter, we need to seek enough sun to main­tain vi­ta­min D pro­duc­tion.

Ques­tion:

How long does vi­ta­min D last in the body? Do we need daily sun ex­po­sure to keep lev­els topped up, or is once a week in the sun suf­fi­cient?

An­swer:

Vi­ta­min D has long been known for its im­por­tant role in bone metabolism. How­ever, mount­ing ev­i­dence links vi­ta­min D lev­els to the sever­ity and fre­quency of res­pi­ra­tory in­fec­tions in chil­dren and ad­verse preg­nancy out­comes. Re­cent re­search also delves into its pos­si­ble links with colon cancer and au­toim­mune dis­or­ders, such as mul­ti­ple sclero­sis and di­a­betes mel­li­tus. But the prob­lem is how to bal­ance vi­ta­min D pro­duc­tion in the body with pro­tect­ing our skin from sun dam­age?

Vi­ta­min D is found in small amounts in foods such as oily fish – for ex­am­ple, salmon, tuna, sar­dines, eel and ware­hou – milk, dairy prod­ucts, eggs and liver. Some mar­garines, spreads, dairy sub­sti­tutes and liq­uid-meal prod­ucts also con­tain added vi­ta­min D.

How­ever, food sources don’t meet our vi­ta­min D needs, which leaves us de­pen­dent on our skin pro­duc­ing vi­ta­min D when ex­posed to sun­light. Un­for­tu­nately, that same ex­po­sure can dam­age our skin.

Pamela von Hurst, the co-di­rec­tor of Massey Univer­sity’s vi­ta­min D re­search cen­tre and an ad­viser to the Min­istry of Health, says the vi­ta­min lasts just over a month. “Some re­search shows it has a half-life of up to 90 days, but other stud­ies show a half-life of 28 days.” A pos­si­ble rea­son for the wide dis­par­ity may be vari­a­tions in in­di­vid­ual health and di­etary in­take, she says.

“If your cal­cium in­take is re­ally low, you’re go­ing to be us­ing a lot more vi­ta­min D be­cause it’s go­ing to be re­quired for all the roles that it has around reg­u­lat­ing cal­cium lev­els. If you’re ill, you’ll use a lot more vi­ta­min D,” says von Hurst.

Our body’s abil­ity to stock­pile vi­ta­min D may partly ex­plain why South Is­lan­ders tend to have sim­i­lar vi­ta­min D lev­els to people in other re­gions, even if they are ex­posed to lower ul­tra­vi­o­let ra­di­a­tion lev­els in win­ter. “South Is­lan­ders build up re­ally good stores in sum­mer. They get a lot more sun – as a rule it’s a lot warmer, sun­nier and drier in sum­mer than it is in the north.”

So, how much sun ex­po­sure should we aim for to op­ti­mise our vi­ta­min D lev­els without en­dan­ger­ing our skin? “Fre­quent, brief ex­po­sure would be the rec­om­men­da­tion, and never put your­self at risk of burn­ing,” says von Hurst.

In win­ter, ex­pose your arms, face and neck dur­ing the mid­dle of the day. About 30 min­utes is ideal and un­likely to cause sun­burn. “Go for a nice brisk walk that warms you up

and you’re more in­clined to bare a bit of skin,” says von Hurst.

“In the South Is­land, the sun is strong enough that you’ll still make vi­ta­min D. But given the weather’s of­ten not sunny and it’s of­ten too cold to ex­pose enough skin, per­haps some sup­ple­men­ta­tion in ad­di­tion to sun ex­po­sure is ad­vis­able through win­ter.”

The max­i­mum dosage of vi­ta­min D sup­ple­ment avail­able over the counter is 1000IU, says von Hurst. “Any­one who is at risk of a de­fi­ciency should be tak­ing 2000IU daily for the sake of their bones.”

Between Septem­ber and April, sun pro­tec­tion is rec­om­mended – shade, a hat and cloth­ing that screens the face and neck, along with sun­screen and sun­glasses – es­pe­cially between 10am and 4pm. A daily walk is still a good idea, but in­stead of mid­day, aim to be out­doors in the early morn­ing or late af­ter­noon.

Von Hurst has the per­fect so­lu­tion for her sun ex­po­sure this win­ter. She’s go­ing to Spain for an in­ter­na­tional vi­ta­min D work­shop in Barcelona to present find­ings from a re­cent clin­i­cal trial in­ves­ti­gat­ing links between autism and lev­els of vi­ta­min D and omega-3. Although she can’t yet re­veal the re­search find­ings, she says the trial pro­duced some, “quite in­ter­est­ing re­sults”.

In win­ter, ex­pose your arms, face and neck for about 30 min­utes dur­ing the mid­dle of the day.

Pamela von Hurst: vi­ta­min D lasts about a month.

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