# Sunshine, vitamin D, and showering: what's the real deal? **URL:** \ **Category:** Factual Questions\ **Created:** [May 16, 2009, 3:23am UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609 "2009-05-16T03:23:18Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [May 18, 2009, 5:09pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/21 "2009-05-18T17:09:17Z")
> [@Broomstick](#): > > On the other hand, sunglasses reduce your chances of getting cataracts. Granted, those are curable these days. > > Really, it seems obvious to me that people evolved to get most of their vitamin D from sunlight. There should be a happy medium between “sunscreen all the time” and “no sunscreen at all” that allows one to minimize skin cancer while maximizing vitamin D. This would be partly dependent on one’s quantity of skin pigment so a blanket recommendation probably couldn’t be made, but surely there is a way to to come up with a sliding scale. There is a happy medium, though I don’t know how easily quantified it is. Skin cancers are most prevalent on people who get really high doses of UV, often to the degree of sun burn (though a burn is certainly not necessary). Furthermore, if you’re out doing normal\* activities - gardening, hiking, etc. - then you’re probably moving through patches of sun and shade and not just lying out under the sun. - Normal defined as behaviors that are closer to what hunter-gatherer ancestors probably did. ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [May 18, 2009, 5:36pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/22 "2009-05-18T17:36:10Z")
I’ve ordered a bunch of textbooks from the early 30’s recently, because I was curious about what my grandmother would have learned in high school. Answer: drink a shitload of milk and get out in the damned sun! (Also, you need to be gaining more weight - gotta chart that shit! Turn to the back of the book for normal weight gain charts for tall, medium, and short girls and boys!) Seriously, every book I’ve gotten so far except for the American history one had something in it about getting enough sunlight, and take some cod liver oil just in case. ---
**Author:** ![gigi](https://avatars.discourse-cdn.com/v4/letter/g/a587f6/32.png) [@gigi](https://boards.straightdope.com/u/gigi)\ **Post date:** [May 18, 2009, 8:51pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/23 "2009-05-18T20:51:55Z")
> [@Markxxx](#): > > Of course if people would just eat a bowl of “Total” cereal…🙂 Could I just eat fifteen bowls of Crispix instead? ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [May 18, 2009, 11:16pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/24 "2009-05-18T23:16:27Z")
> [@Ro0sh](#): > > But yeah- okay, if you’re not getting the 20 mins of sunlight- then you need to think about supplements, but in that case ordinary Vitamin D wouldn’t help you- you’d need the ACTIVATED form of Vitamin D3, which have a half life if I recall of around 20 days to a month- because if it’s the sunlight that’s an issue that’s a step in the Vitamin D activation, getting the inactive form orally does nothing for you if Sunlight’s the problem. So if you’re supplementing yourself, make sure you’re getting the right form that you need: cholecalciferol. It seems you are mistaken. “Activation” happens in the liver and kidneys, after the sun’s done its work. The body can activate the ordinary supplemental D3 without the sun. [http://ods.od.nih.gov/factsheets/vitamind.asp](http://ods.od.nih.gov/factsheets/vitamind.asp) ---
**Author:** ![J\_n3t](https://avatars.discourse-cdn.com/v4/letter/j/ec9cab/32.png) [@J\_n3t](https://boards.straightdope.com/u/J_n3t)\ **Post date:** [January 15, 2012, 5:43pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/25 "2012-01-15T17:43:45Z")
I would think that inflammation would be the primary problem for maintaining adequate VitD levels: Considering that VitD precursor is activated in the two innermost dermal strata, I just can’t get my mind around the idea a shower would interfere - its not like you are washing off sunshine. Use a mild soap, and don’t linger. Sitting in a bubble bath for extended periods could concievably interfere with the production of VitD, but not a shower, esp a nice warm one ([http://hwmaint.jbc.org/cgi/content/full/270/15/8706](http://hwmaint.jbc.org/cgi/content/full/270/15/8706)). > [@](#): > > J Invest Dermatol. 1981 Jul;77(1):51-8. > The cutaneous photosynthesis of previtamin D3: a unique photoendocrine system. > Holick MF. > Abstract > > The skin has been recognized as the site for the sun-mediated photosynthesis of vitamin D3; until recently, however, very little was known about either the sequence of events leading to the formation of vitamin D3 in human skin or the factors that regulate the synthesis of this hormone. It is now established that, during exposure to sunlight, the cutaneous reservoir of 7-dehydrocholesterol (principally in the stratum Malpighii) converts to previtamin D3. Once this thermally labile previtamin is formed, it undergoes a temperature-dependent isomerization to vitamin D3 over a period of 3 days. The plasma vitamin-D binding protein preferentially translocates vitamin D3 from the skin into the circulation. During prolonged exposure to the sun, the accumulation of previtamin D3 is limited to about 10 to 15% of the original 7-dehydrocholesterol content because the previtamin photoisomerizes to 2 biologically inert photoproducts, lumisterol3 and tachysterol3. Increases in either latitude or the melanin concentration in the skin diminish the epidermal synthesis of previtamin D3. A single total body exposure to 3 minimal erythemal doses of ultraviolet radiation increased the vitamin-D3 levels in the serum 25-hydroxyvitamin-D levels after 7 days. The unique mechanism for the cutaneous synthesis, storage, and steady release of vitamin D3 into the circulation prompted an investigation into the potential therapeutic benefits of using the skin as the site for the synthesis and absorption of vitamin-D3 metabolites. On the other hand, as humans have changed their diet from whole foods to processed foods and are now consuming large quantities of animal products (raised in unnatural ways), we have changed our consumption of omega-3 and omega-6 from a ratio of 1:4 to 1:17. We are afflicted with diseases of inflammation (cardiovascular, diabetes, cancer, etc), which increases our need for Vit D. > [@](#): > > Joint Bone Spine. 2010 Dec;77(6):552-7. Epub 2010 Nov 9. > Vitamin D and inflammation. > Guillot X, Semerano L, Saidenberg-Kermanac’h N, Falgarone G, Boissier MC. > Source > > EA4222, Li2P, PRES Paris-Cité, université Paris 13, 93000 Bobigny, France. [xavier.guillot@avc.aphp.fr](mailto:xavier.guillot@avc.aphp.fr) > Abstract > > Calcitriol, or 1,25-dihydroxyvitamin D3 (1,25(OH)(2)D3) is a well-known endocrine regulator of calcium homeostasis. More recently, local calcitriol production by immune cells was shown to exert autocrine or paracrine immunomodulating effects. Immune cells that produce calcitriol also express the vitamin D receptor (VDR) and the enzymes needed to metabolize vitamin D3 (1α-, 25-, and 24-hydroxylases). Studies of animal models and cell cultures showed both direct and indirect immunomodulating effects involving the T cells, B cells, and antigen-presenting cells (dendritic cells and macrophages) and affecting both innate and adaptive immune responses. The overall effect is a switch from the Th1/Th17 response to the Th2/Treg profile. The immunomodulating effects of vitamin D may explain the reported epidemiological associations between vitamin D status and a large number of autoimmune and inflammatory diseases. Such associations have been suggested by observational studies not only in rheumatoid arthritis, lupus, inflammatory bowel disease, and type 1 diabetes; but also in infections, malignancies, transplant rejection, and cardiovascular disease. In animal models for these diseases, vitamin D supplementation has been found to produce therapeutic effects. Thus, vitamin D is a key focus for public health efforts and may hold promise for the treatment of dysimmune diseases. I would advise maintaining acceptable levels of hygiene using a mild soap - then research the effect of diet on inflammation. ---
**Author:** ![chappachula](https://avatars.discourse-cdn.com/v4/letter/c/d2c977/32.png) [@chappachula](https://boards.straightdope.com/u/chappachula)\ **Post date:** [January 15, 2012, 6:01pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/26 "2012-01-15T18:01:02Z")
what is this “20 minutes of sunshine per day” requirement? how much exposure do you need? is it 20 minutes of full-body exposure, like lying on a beach in a bikini? or 20 minutes of exposing one arm (like driving a car with one arm resting in the side window, wearing a short sleeve shirt) Because I’ll bet that on most days, the vast majority of people don’t get _ANY_ exposure to the sun. If you live in a house with a garage, or an apartment with a shaded carport, drive to work in an office, then drive home, with a stop at Walmart, then drive the kid to her swimming lesson at the YMCA’s indoor pool, etc…you will not be outdoors for more than 2-3 minutes total. And if you are wearing normal street clothes, your entire body is covered up for those few minutes. (yes, I just noticed that this thread is 3 years old …but, hey, sunshine doesn’t have a shelf life…) ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 15, 2012, 6:42pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/27 "2012-01-15T18:42:28Z")
> [@chappachula](#): > > what is this “20 minutes of sunshine per day” requirement? … Generally they are talking about dressed in shorts and a tanktop. (I wonder if **QtM** would be up for updating us on more recent developments regarding Vit D?) ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [January 16, 2012, 2:31am UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/28 "2012-01-16T02:31:32Z")
> [@DSeid](#): > > Generally they are talking about dressed in shorts and a tanktop. > > (I wonder if **QtM** would be up for updating us on more recent developments regarding Vit D?) Until he stops by, I can comment that my GP routinely tests for Vit D levels, and told me that a high (unspecified) percentage of his patients test low. He starts people on 5000 IU for three months, and then retests. In my case, we dropped to 1000 IU, but he wasn’t happy with my readings. We settled on 2000 IU. Your mileage and body may differ. -D/a ---
**Author:** ![robinson](https://avatars.discourse-cdn.com/v4/letter/r/848f3c/32.png) [@robinson](https://boards.straightdope.com/u/robinson)\ **Post date:** [January 16, 2012, 7:24am UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/29 "2012-01-16T07:24:22Z")
IIRC 20 min sunlight is 10,000 IU, and the RDA is only about 100. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [January 16, 2012, 9:45am UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/30 "2012-01-16T09:45:37Z")
If zombies showered it’d probably wash off their vitamin D, and some other important bits. ---
**Author:** ![bardos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bardos/32/1069_2.png) [@bardos](https://boards.straightdope.com/u/bardos)\ **Post date:** [January 16, 2012, 1:51pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/31 "2012-01-16T13:51:35Z")
> [@robinson](#): > > IIRC 20 min sunlight is 10,000 IU, and the RDA is only about 100. a cite for this 100iu as RDA that is not a government quack.? ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 16, 2012, 8:36pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/32 "2012-01-16T20:36:21Z")
While the actual [numbers advised by the government hacks](http://www.nal.usda.gov/fnic/DRI//DRI_Calcium/250-287.pdf) are, I think, 200 IU up to age 50 and 400 51 and over, and there is great room for debate over what the numbers should be, one wonders if your definition of “hack” is anyone who supports a claim you disagree with. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [January 17, 2012, 12:32am UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/33 "2012-01-17T00:32:42Z")
We’re still scratching our heads over whether or not more people should be taking higher doses of vitamin D since the last time I posted extensively on this subject. some recent updates from [UpToDate.com](http://UpToDate.com): > [@](#): > > **Muscular**. A causal relationship between vitamin D supplementation and improvement in muscle weakness has not been demonstrated in randomized trials and the optimal 25OHD concentration for muscle function is unknown. Any benefit of vitamin D supplementation on muscle strength is likely to occur in patients with baseline 25OHD levels below 10 or 20 ng/mL (25 or 50 nmol/L). > [@](#): > > **Cancer**. Although some data suggest an association between vitamin D deficiency and cancer, the direction of the association may depend upon the serum 25OHD concentration. The evidence is insufficient to support large dose vitamin D supplementation for cancer prevention or treatment > [@](#): > > **Immunology**. There are conflicting reports on the association between vitamin D status and allergic diseases. In some reports, vitamin D deficiency (in pregnant women, children, or adolescents) has been associated with increased as well as with decreased frequency of allergic diseases such as asthma or eczema. > [@](#): > > **Diabetes**. Vitamin D status is lower in individuals with type 2 diabetes, but the causality of this relationship is unknown. Poor vitamin D status is also frequently linked with nearly all elements of the metabolic syndrome, but the existing intervention studies are either negative or showed only limited beneficial effect. > [@](#): > > **Cardiovascular:** In a review of four interventional randomized trials and a meta-analysis of six trials, however, there was no effect of supplementation on cardiovascular outcomes, including myocardial infarction and stroke. The meta-analysis also did not show a significant effect of vitamin D supplementation on cardiovascular risk factors (lipids, glucose, blood pressure). In one of the larger trials included in the meta-analysis, there was no beneficial effect on cardiovascular or metabolic risks after increasing baseline 25OHD levels from 23 to well above 40 ng/mL (58 to 100 nmol/L) . Thus, the causal nature of the association between vitamin D and cardiovascular disease remains uncertain. > [@](#): > > **Dosage recommendations for people not suspected of having a deficiency**. Vitamin D supplementation (700 to 1000 Units/day) reduces the risk of falls in elderly populations. However, a causal association between poor vitamin D status and nearly all major diseases (cancer, infections, autoimmune diseases, cardiovascular and metabolic diseases) has not been established. So, we still don’t know a lot more than we do know. But the rush to go out and take megadoses of Vitamin D is not supported by evidence at this time. 800-1000 U a day makes sense if you are older and don’t get much sun. And it sure won’t hurt to dose yourself in that range if you’re younger, but the benefit of that dose hasn’t been proven for that age group. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [January 17, 2012, 6:05pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/34 "2012-01-17T18:05:05Z")
Thank you. ---
**Author:** ![Renee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/renee/32/287_2.png) [@Renee](https://boards.straightdope.com/u/Renee)\ **Post date:** [January 17, 2012, 6:52pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/35 "2012-01-17T18:52:32Z")
**Qadgop the Mercotan** , just curious, do those studies tend to be looking at the effects of supplementation via either pills or injection (if they even do that?) Or are they looking at supplementation via increased actual sunlight? ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [January 17, 2012, 6:54pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/36 "2012-01-17T18:54:31Z")
> [@Renee](#): > > **Qadgop the Mercotan** , just curious, do those studies tend to be looking at the effects of supplementation via either pills or injection (if they even do that?) Or are they looking at supplementation via increased actual sunlight? Pills. ---
**Author:** ![bardos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bardos/32/1069_2.png) [@bardos](https://boards.straightdope.com/u/bardos)\ **Post date:** [January 17, 2012, 8:52pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/37 "2012-01-17T20:52:13Z")
> [@DSeid](#): > > While the actual [numbers advised by the government hacks](http://www.nal.usda.gov/fnic/DRI//DRI_Calcium/250-287.pdf) are, I think, 200 IU up to age 50 and 400 51 and over, and there is great room for debate over what the numbers should be, one wonders if your definition of “hack” is anyone who supports a claim you disagree with. quack really. not hack Check out this video which is one of a multitude of videos about Vitamin d (d3)which does not carry ancient government information as to the dangers of Vitamin D https://www.youtube.com/embed/qeg-5NDyJ84?feature=oembed&wmode=opaque I have been taking 5000iu of D3 daily for about a year and have not been sick one day over this period although as a teacher I am exposed to a myriad of sneezes coughs and germs in general. ymmv ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [January 17, 2012, 9:15pm UTC](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609/38 "2012-01-17T21:15:53Z")
> [@bardos](#): > > quack really. not hack > > Check out this video which is one of a multitude of videos about Vitamin d (d3)which does not carry ancient government information as to the dangers of Vitamin D > > [http://www.youtube.com/watch?v=qeg-5NDyJ84](http://www.youtube.com/watch?v=qeg-5NDyJ84) > > I have been taking 5000iu of D3 daily for about a year and have not been sick one day over this period although as a teacher I am exposed to a myriad of sneezes coughs and germs in general. > > ymmv Yes, youtube videos and personal testimony is the best source of health information there is… [Previous page](https://boards.straightdope.com/t/sunshine-vitamin-d-and-showering-whats-the-real-deal/496609.md?page=1)