How much sunshine does it take to make enough vitamin D? Perhaps more than you think!
There's been a lot of hand-wringing lately about people not getting enough vitamin D. Deficiency is quite common--especially among kids, the elderly, and those with dark skin. And a growing list of diseases and conditions are being linked with vitamin D deficiency.
Regular sun exposure, without sunscreen, causes your skin to produce vitamin D naturally.
How much sun does it take to satisfy your vitamin D requirements?
If you've read anything about this, you've probably seen some vague guidelines, recommending "a few minutes every day." But these recommendations are far too general to be useful. The amount of sun you need to meet your vitamin D requirements varies hugely depending on your location, your skin type, the time of year, the time of day, and even the atmospheric conditions.
A Cool Tool: The vitamin D/UV calculator
Scientists at the Norwegian Institute for Air Research have devised a calculator that will take all those factors into consideration and estimate how many minutes of exposure you need for your skin to produce 25 mcg (the equivalent of 1,000 International Units) of vitamin D.
It's a very cool tool and the best I've seen so far. Be forewarned: It's not the most user-friendly interface and its very easy to enter the wrong information, which makes your results misleading. But once you get past the technicalities, it's very interesting to see how much the answers change when you vary the input.
Here are some tips to help you get good results.
1. Unless you live in one of a few European or African cities listed as options, you'll need to determine your latitude and longitude. A GPS device will tell you your lat/long. You can also find this information on Google Earth. Here's also a list of lat/longs for lots of American cities. VERY IMPORTANT: The program reads all latitudes as N and all longitudes as E. If your latitude is 39 S, enter -39. If your longitude is 76 W, enter -76. (It took me forever to figure out this quirk!) Also, be sure to click the radio button next to your latitude and longitude entries. It is not automatically selected when you fill in these values.
2. You also need to estimate your complexion, and the options include both "blond" and "pale," which is a little confusing. (Maybe it makes more sense to Norwegians). Basically, the six categories are arranged from lightest (pale) to darkest (black). Make your best guess based on that. I have dark eyes and hair so I chose "darker caucasian."
3. Enter the time of day you are going out in the sun, expressed as UTC (aka Greenwich Mean Time). Here is a converter that will convert local time into UTC. The calculator uses a 24 hour clock, so hours from 1pm to midnight are expressed as 13 to 24. There is also an option that lets you choose "about midday." If you enter an actual time, be sure to click the radio button next to your start time. It doesn't move automatically when you fill in these values.
4. Next, enter how much cloud cover there is. If you choose "overcast," you can also enter in the UV Index from your local newspaper's weather page and the program will estimate the thickness of the cloud deck. Again, be sure to click the radio button if you choose this option. (Disclaimer: I played around with this and couldn't see that changing the UV index had any effect...)
5. You're almost done! Next, the calculator wants to know the thickness of the ozone layer. I have to admit, I was unable to find a simple resource to help with this one. Unless you live under the ozone hole or have some other way of knowing that the ozone is particularly thick or thin where you are, I suggest just setting this one to medium.
6. Find your altitude. Some GPS devices can tell you your altitude, as can Google Earth or topographical maps. But the easiest way may be to simply google "altitude of [your town]". Remember to convert it to kilometers. One kilometer = about 3300 feet.
7. Choose your surface.
Here's what my form looks like all filled in:
When I submit it for calculation, I learn that here in Baltimore, on a cloudless August day at noon, I need to spend just 5 minutes with my face, hands, and arms exposed to produce 25 mcg (1,000 IU) of vitamin D. If it were November, I'd need to stay out about half an hour. If it were November, and I were black, it would take an hour and a half. You get the idea. For most of the year, "a few minutes" of sun would not be enough for me to make enough vitamon D.
Keep in mind that these exposure times are considered enough to maintain healthy vitamin D status. if you are starting out with a vitamin D deficiency, you might need more.
One last thought: Unprotected sun exposure also increases the risk of skin cancer and premature aging of the skin. After you've gotten your daily "dose," I recommend applying a good sunscreen!
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Posted by: Rodney Brooks | Oct 29, 2009 12:41:46 PM
Sunshine = Vitamin D = better health but within limits.
Posted by: nutrition sportive | Oct 29, 2009 3:26:23 AM
I finally decided to write a comment on your blog. I just wanted to say good job. Its nice informative post.
Posted by: Gina | Oct 15, 2009 11:17:46 PM
Can a tanning bed help you produce vitamin D and if so how long and often would you have to lay as a light skinned individual to get enough?
Posted by: Gina | Oct 13, 2009 6:57:02 PM
I have been told that you can not produce any vitamin D in the winter in St. Louis, MO because the sun's rays are tilted at a different angle in the winter.
Monica's Response: Well, if you're out there at 8 in the morning on a cloudy day I think you're right. But, according to the calculator that I talked about in a recent post, on December 20th at noon on a cloudless day in St. Louis, standing on dry concrete with your face, arms, and neck exposed, it would take 48 minutes every other day for your skin to absorb enough UV to produce sufficient vitamin D. You can plug in different variables (different day, different time, different weather, etc.) and see how it changes the result. Instructions for using the calculator are on this post:
http://blog.nutritiondata.com/ndblog/2009/08/how-much-sunshine-does-it-take-to-make-enough-vitamin-d.html
Posted by: recettes minceur | Oct 6, 2009 8:39:51 AM
It is interesting to read your comments that sunshine is the only effective way to produce sufficient vitamin D in humans. I live in a country where we would love to get more vitamin D but our exposure to sunlight is very limited due to our weather patterns. If I may point out my way of getting sufficient quantities of the vitamin is to take a daily dose of cod liver oil which contains the vitamin. As a spin-off, cod liver oil is rich in omega 3 fatty acids which as we know has great health benefits.
recettes minceur
Posted by: Bethany | Sep 21, 2009 3:25:12 PM
Monica and Lydia, thanks for the responses. When we can't get outside every day, it's good to know that make-up days can suffice within a reasonable period of time.
Posted by: NYCnutrition | Sep 19, 2009 4:40:55 PM
uh...great tool, and I'll have to give the creators a pass since they're Norwegian, but don't they realize that there's far greater variation in Middle Eastern and Black complexions than in caucasian? yet there are 3 options for caucasian...
Posted by: Lydia | Sep 12, 2009 8:33:09 PM
Can Vitamin D be "stored?" I.e. if you exceed recommended exposure on a given day, can you (or should you) stay in from the sun the next? Poster (Bethany) asked this in a previous post but I also couldn't find an answer posted.
Monica's Response: Vitamin D can be stored but, as far as I can tell, not more than a couple of weeks. But if your vitamin D stores are topped off, you won't "overdose" by being in the sun. Your skin stops producing vitamin D.
Posted by: Monica Reinagel | Sep 1, 2009 6:38:26 AM
UPDATE: there have been assertions that washing the skin after sun exposure could "wash off" vitamin D. I took the question to Michael Holick, one of the world's foremost authorities on vitamin D. Dr. Holick responds that vitamin D is produced in living cells and cannot be washed off.
Posted by: Norwegian by descent, yah. | Aug 27, 2009 11:49:04 PM
Oh, yes. The blond versus pale distinction makes sense. My daughter is blond, with rosy cheeks and creamy ivory skin, little freckles across her nose. I, on the other hand, am pale. So pale, in fact, that my bare back looks like a road map, and you can see the little blue veins through the skin on the tops of my cheekbones.
Posted by: Jason M | Aug 25, 2009 11:08:26 AM
Larry,
in the case of Kale for Vitamin A, to get 100g of cooked Kale (greens such as spinach and kale are important to cook) this would be about 2 cups of raw kale, and this does not even give you half of the vitamin a you claim we need. And just because you have this intake does not mean all of it is absorbed or utilized properly. Relying on plant foods is just not a good way to get the vitamin a required. Carotenes are also better converted when in the presence of true vitamin a (retinol), and MUST be eaten with Fat, as they are fat soluble vitamins.
Posted by: Jason M | Aug 25, 2009 10:59:35 AM
Larry M,
RDA is the mistake. The current recommendation for Vitamin D is 200-400IU. EXTREMELY LOW! Basically every single scientist who has an opinion on this recommends a minimum of 1000IU, and at least 4000IU a day for optimum heath. Some even call for 10,000IU but that is a little excessive sounding, however, it couldn't hurt for people to get outside a little bit more often to accomplish part of the requirements.
"The Dietary Reference Intake (DRI) Recommended Daily Amount (RDA) for Vitamin A for a 25-year old male is 900 micrograms/day, or 3000 IU.
The ratio of conversion of β-carotene to vitamin A has changed over time from 6:1 to 12:1 and currently is estimated to be 21:1 from recent studies and experimental trials carried out in the developing nations. The implication of the current ratio is that large quantities of β-carotene are needed for conversion to yield the desired dietary requirement of vitamin A for deficient group of the population. This also means that more continents are now being affected by the deficiency of vitamin A, not just the peculiar ones (Africa and Asia)."
Vit A Yield (IU/100g)
Sweet Potatoes 1,500
Turkey Giblets 35,800
Carrots 1,145
Beef Liver 25,800
Kale 1,295
CLO (1/2 tsp) 5,750
Spinach 997
Eggs 570
Collard Greens 770
Butter 330
As you can see the conversion process of carotenes to true Vitamin A is extremely bad. Fermented cod liver oil does not just have retinol, it has numerous other co-factors and substrates. Fermented CLO is a good source of both Vitamin D2 and Vitamin D3, amongst other forms. To say that we should not be getting more than 3000IUs a day of Vitamin A in the form of retinol is ridiculous. This would throw the whole idea of our grandparents and every generation before of eating liver and organ meats regularly, even once a week, as they are VERY good sources of Vitamin A. Also, the ratio between Vitamin A and Vitamin D should be approximately 10:1 on average, so if scientists are recommending we get 4000IU, then you do the math. This isn't to say we need that exact amount to be in absolute perfect health each day. Vitamin K2 also plays a major role in bone health. This can only be found in properly fermented foods like natto and saurkraut, as well as animal fats. (i.e Goose liver being hte highest! Way to go French) And saturated fats help to apply calcium in the bones.
So when you see the bag of baby carrots with a vitamin A percentage of 300% for 1/2 cup or something along those lines, that is complete hogwash!
POSTED BY: TOM | AUG 24, 2009 12:45:20 PM
Hemp seed contains about 2200 IU of Vit. D per 100g. The only wholesome food source I know of.
This would be Vitamin D2, which is what milk used to be fortified with (because of pasteurization) and lack of real foods in the diet, and the rise of industrial food. Vitamin D3 is now used as it was found that high amounts of Vitamin D2 was toxic and actually blocked the uptake of Vitamin D. So Hemp seeds are not the best source by far, and they should be toasted to help reduce the seed preservatives which can block nutrient absorption in the intestines.
Posted by: Larry M | Aug 24, 2009 8:31:28 PM
Jason M above posted a bit of misinformation about vitamin A. The retinyl form of vitamin A (found in cod liver oil) has a narrow optimal range around 3000 units per day. Intake values above perhaps 5000 units and below about 2000 units have been shown in several studies to cause a decrease in bone mineral density and an increase in the number of fractures. A toxic syndrome marked by bone pain can occur at doses of 20,000 units a day, if taken over a period of weeks, during which the fat soluble vitamin will accumulate in the body. Cod liver oil is not to be recommended as a long term source of vitamin D.
Posted by: Chef Jan | Aug 24, 2009 5:23:31 PM
I just calculated it for today in Houston, TX and the number is 2 minutes. There is nothing quite like the sun in Texas. Just enough humidity on the gulf to keep us from getting crisp.
Monica's Response: Yes, it doesn't take much at high noon during the summer months. But it's interesting to see how much MORE you need in the winter, or if your exposure is at 8am or 4pm rather than noon.
Posted by: Andrea | Aug 24, 2009 1:22:44 PM
Thank you for your article! This topic has recently become a real concern for me. I had to have a thyroidectomy 2 weeks ago and along with that a lot of blood draws to check my calcium levels. It was discovered that my calcium levels were disturbingly low and when my physician looked at blood work results from 3 years ago found that it was very low then as well, which indicates it has probably been an issue for quite some time I just didn't know about it. We are now trying to determine the cause for the low calcium and a lack of vitamin D is certainly being checked. Thank you for your helpful information.
Posted by: Bethany | Aug 24, 2009 1:07:16 PM
Not sure if someone's already asked this, but I'm wondering if it counts to accumulate sun exposure over a certain amount of time.
For example, if I need 60 minutes outside on a typical Pittsburgh afternoon, can I fullfill my requirement with 120 minutes one day and zero the next?
Would be nice if the requirement could be filled weekly so weekends can be used to catch up on housework AND vitamin D production.
Posted by: Tom | Aug 24, 2009 12:45:20 PM
Hemp seed contains about 2200 IU of Vit. D per 100g. The only wholesome food source I know of. Here is a link to a web sight that displays the UV index for various locations. http://exp-studies.tor.ec.gc.ca/e/ozone/uv_plots.htm
Posted by: Jason M | Aug 21, 2009 6:01:23 PM
The only supplementation people should be taking is from WHOLE FOOD SUPPLEMENTS. i.e. cod liver oil, dessicated liver and organ pills, acerola tablets, etc
Vitamin pills fall in line with the reductionist science point of view. The complex chemistry of food is your best source of life, not a pill.
Posted by: Jason M | Aug 21, 2009 5:57:18 PM
Natural Vitamin A from sources like cod liver oil is not toxic unless you are regularly consuming a CUP of cod liver oil! In excess of 50,000IU it can be a problem if you are taking this each day, unless you are recovering from surgery, etc. It could be helpful then for short periods. SYNTHETIC Vitamin A can be quite toxic at lower levels.
Vitamin A and D and K2 work together. You need a ratio of approximately 10 to 1 (Vitamin A to Vitamin D). K2 still needs a lot more studies. There are so many different kinds of K2 (i.e MK-7 from fermented foods, and MK-4 from animal fats) These are the two you need the most.
There are also other substances in and benefits of traditionally fermented cod liver oil! (MOST commercial brands nowadays filter the oil so much and then add synthetic vitamins back in, and not even at good ratios! i.e. Carlsons and the like)
OH, and the Vitamin D that mushrooms can produce is Vitamin D2, what they use to 'fortify' commercial milk with, until they found it to be toxic at certain levels, AND actually blocked your bodies receptors for Vitamin D3 which is what your body produces from cholesterol when the sun hits your skin at certain angles/intensities, AND Vitamin D3 is only found in animal fats (i.e. pastured lard and tallow, cod liver oil, etc.)
Posted by: Monica Reinagel | Aug 21, 2009 4:01:28 PM
I, too, am suspicious about the washing off thing. Let me see if I can get an expert opinion. Stay tuned.
Posted by: kelly | Aug 21, 2009 3:54:46 PM
Don't wash for 24-48 hours after sun exposure? So to get your daily (24 hours) exposure, then you can never shower or wash your hands. That would mean you could "wash off" a sunburn too.
Posted by: PE | Aug 20, 2009 2:50:54 PM
I'd read about not washing after exposure, but others have said that, since (if?) vitamin D precursors are deeper than the surface skin layer, there's no way to wash them off. True?
Posted by: Julie | Aug 20, 2009 1:05:50 PM
I just wanted to add that it's very important that the skin is not washed with soap for 24-48 hours after exposure. The skin actually takes time to absorb the newly synthesized vitamin D into the bloodstream. This isn't a problem when people are outside for long periods of time and synthesize much higher amounts, but if you are outside simply to get the bare minimum, you need to make sure you aren't washing it off - literally.
Posted by: worley | Aug 17, 2009 10:02:23 AM
good info. here is another good article for sun exposure.
http://articles.mercola.com/sites/articles/archive/2008/09/04/when-should-you-go-out-in-the-sun.aspx
Posted by: Stephanie | Aug 14, 2009 5:40:54 PM
Cod liver oil is just not a good idea, because beside Vitamin D it contains vitamin A at toxic levels. To get the newly recommended levels of vitamin D (up to 5000IU), you'd almost certainly get a Vitamin A overdose.
BTW, there are supplements available now with 5000 IU, unfortunately not in here in Europe.
I live a typical Western lifestyle here in Germany and I used to put sunscreen on if I was outside. I used to think just sitting in the car will make Vitamin D, but any glass filters out UVB rays, so no Vitamin D even though you can tan a bit behind glass.
In March 2007 I went to my doctor with symptoms of rheumatoid arthritis and depression, I'm 39 and slightly overweight. Not obese but still too much. As part of the blood work they did a 25(OH)D and my Vitamin D level was below detection level. That is, they couldn't trace any Vitamin D in my body.
I didn't know much about Vitamin D then so I felt uneasy about the 50.000 - 200.000 IU mega-doses and wanted to try myself with over the counters supplements. I took 4x400IU, thus 1600IU a day and after 4 months my levels had just gone up to a mere 43 nmol/L. So I had a friend from the US send me the 5000s IU which aren't available here and took two a day, with 10.000 IU it took a further 7 months to get my levels up to an acceptable level. I've since learned that overweight people may need more Vitamin D to sustain healthy levels, and that a deficiency is a reason one got fat in the first place. Perhaps a part of the brain is constantly urging the consciousness to produce an appetite signal to increase the chances to get Vitamin D from food.
I've also stopped smoking and switched to the vegan diet and since April this year my symptoms of athritis have all vanished, among other health problems which improved. Haven't lost any weight though but my depression which was very bad transformed to a much lighter stage. The haha's happen again on occasion, crawling out of my gut, much to my surpise:-)
Apart from Vitamin B12 I've dropped the supplements as I'm growing my own delicatessen mushrooms on straw (quite simple after an initial learning curve), and dry them in the summer sun and either grind them with the coffee grinder into a powder to be used as a base for sauces or just adding them to soups and stews. If exposed to UVB-light shortly after harvest, mushrooms produce in their skin, not unlike humans, Vitamin D. This method works for me, my levels are OK now, I combine it with "dash in dash out" sun exposure, with clear sky I stay in the sun (almost) full body exposure for maximum 20 minutes. While the calculator is a very nifty tool, my rule of thumb is: No sunburn and no tanning. By staying fair in skin tone I know I'm not straining it, while producing nice amounts of Vitamin D. The fairer, the faster, so there isn't any incentive to tan.
I've since learned a huge amount about Vitamin D, my severe deficiency came as a huge shock to me, I never imagined to have a problem coming from that corner. I'm just living a normal house/car/work/car/supermarket/house/freetime lifestyle, and I used to think that that would be enough to produce adequate levels of Vitamin D, I'm angry for being bombarded with skin-health advise about protecting against skin cancer, I suspect this accelerated my Vitamin D deficiency and eventually led to what would have been severe health issues with a career of being heavily medicated with serious drugs.
Posted by: Monica Reinagel | Aug 13, 2009 2:44:30 PM
Harold, looks like you'll need to cosy up to some cod liver oil next year!!
Posted by: Harold | Aug 12, 2009 1:56:13 PM
I'm planning on living in Trondheim, Norway next year because I'll go to graduate school there and it said that in December I need 24 hours XD and I'm Hispanic, so I chose Mediterranean skin...
Posted by: jude | Aug 12, 2009 12:20:09 PM
Yes I agree with Mark ..
The sun can be dangerous for skin, cancer, melasma, and
sun damage.
Also many people believe sun can cure acne? not true.
Finally what Supplements would you recommend.
thanks for the info!
Posted by: Mark | Aug 12, 2009 9:58:40 AM
I really dont want to be in the sun. Is supplementation equivalent to sun exposure?
Posted by: Steve | Aug 11, 2009 12:15:38 PM
I believe those are "theraputic" dose levels only for severe deficiency, rickets, etc.
Lately Dr's Holick, Veith, Cannell and more feel no around 5000 IU is best for the "average" person to maintain excellent sufficiency.
Posted by: Monica Reinagel | Aug 11, 2009 11:43:30 AM
Bruce: So, what's all this with the 10,000 to 50,000 IU doses we keep hearing about from Dr. Hollick and Co.?
Posted by: Steve | Aug 11, 2009 11:38:42 AM
Bruce: Yes I've seen similar data in the past. But that's an awful lot of pills to take when just 15-20 minutes in the noon sun on 50% body surface can yield 5000 IU... at just less than 1 MED dose.
Or... just 3-4 minutes in a typical tanning bed (gasp - apologies to the WHO lol) would yield same or more. Again at just below a sunburn inition of 1 MED exposure.
Posted by: Bruce | Aug 11, 2009 11:04:42 AM
Results: The initial mean (±SD) serum 25(OH)D concentration was 28.5 ± 10.8 nmol/L. After 12 mo, the 25(OH)D concentration was 125.6 ± 38.8 nmol/L, and it exceeded 74 nmol/L in 92% of the patients. At every 3-mo follow-up, serum parathyroid hormone was lower than at baseline (P = 0.001). No changes in serum calcium or cases of hypercalcemia were observed at the follow-up assessments. Both mean total urinary calcium and the mean urinary calcium-creatinine ratio increased from baseline at one follow-up time point (P 75 nmol/L. This trial was registered at clinicaltrials.gov as NCT00789503.
Am J Clin Nutr 89: 1132-1137, 2009
Posted by: Bruce | Aug 11, 2009 10:54:11 AM
Research conducted at Winthrop University Hospital in Mineola, New York, has determined that individuals with vitamin D insufficiency need an average dose of 3800 to 5000 international units (IU) per day in order to attain optimal levels. The findings were published in the June, 2008 issue of the American Journal of Clinical Nutrition.
One hundred thirty-eight men and women with baseline serum values of 25-hydroxyvitamin D [25(OH)D] of less than 80 nanomoles per liter (nmol/L) were included in the current study. Optimal levels of 25(OH)D have been proposed to be at least 75 nanomoles per liter by U.S. experts, with an upper limit of 220 nmol/L. In order to determine the amount of supplemental vitamin D3 necessary to achieve this concentration, participants whose serum concentrations of the vitamin were greater than 50 nmol/L were started on 2,000 IU per day or a placebo, and those whose levels were below 50 nmol/L were given 4000 IU or a placebo. Follow up visits occurred at eight week intervals over the six month study period, during which serum vitamin D levels were assessed and vitamin D dosage adjusted accordingly.
All of the subjects who received vitamin D were able to attain the target level by the end of the study. No evidence of toxicity of the doses administered was observed. The authors note that the selection of 2000 IU vitamin D per day as a safe tolerable upper intake level by the Food and Nutrition Board is now considered to be based on insufficient evidence. According to the current study's findings, the Conclusions: Determination of the intake required to attain serum 25(OH)D concentrations >75 nmol/L must consider the wide variability in the dose-response curve and basal 25(OH)D concentrations. Projection of the dose-response curves observed in this convenience sample onto the population of the third National Health and Nutrition Examination Survey suggests a dose of 95 µg/d (3800 IU) for those above a 25(OH)D threshold of 55 nmol/L and a dose of 125 µg/d (5000 IU) for those below that threshold.
American Journal of Clinical Nutrition, Vol. 87, No. 6, 1952-1958, June 2008
Posted by: Steve | Aug 11, 2009 9:09:00 AM
There is a lot easier way than that to find real-time D3 IU: The Solartech Model 6.4 Solarmeter® as seen on www.solarmeter.com .
It comes with an interactive excel spreadsheet to adjust for skin type, age, tan level, and percent body exposure.
The calculator from Norway appears too conservative. At this time of year mid latitude USA near solar noon it would take about 15 minutes (not 5) to synthesize 1000 IU on 10% body (face, hands, forearms) for type 2 skin.
Monica's Response: Nice thing about the calculator is that it's free.
Posted by: Pete | Aug 11, 2009 4:48:10 AM
This calculator is for 1000iu but the body consumes about 5000iu a day, if it is available. Unfortunately just increasing the time will not help, you need to expose more skin. If you only need 5 minutes sun a day how come most of the USA's children are vitamin d deficient?
Monica's Response: In my example, it takes 5 minutes a day at noon in August at 39 degrees latitude--most of the year (and/or further north or further from midday) it takes significantly more.
Do you have a reference for the fact that the "body consumes about 5000IU a day"?
Posted by: Jasmine | Aug 10, 2009 9:37:20 PM
There's no selection for cities in Asia such as Hong Kong or Tokyo? I am not a caucasian but I am quite fair...seems this calculator is only for caucsian and those live in Europe...
Monica's Response: No North American cities either! Most people will need to look up their latitude and longitude in order to use this calculator.
Posted by: Steve Parker, M.D. | Aug 10, 2009 8:30:13 PM
It's easy to see now why many people just take a vitamin D supplement, 400 to 1000 International Units daily, and be done with it.
Getting outdoors in the sun probably has lots of other benefits anyway. E.g., improved mental health.
Posted by: EL | Aug 10, 2009 8:02:43 PM
Just two minutes at midday in Tampa, FL, in the middle of August for a pale caucasian. Eleven minutes in December. That's a lot less than I thought.
Monica's Response: I think that people living in Northern cities like Chicago or Seattle will be suprised, though, at how much they'll need in the fall and winter.
Posted by: Monica Reinagel | Aug 10, 2009 7:49:18 PM
Olwen, the results specify that the time is based on exposed arms, face, and hands. If you have less or more skin showing, you'd need to adjust accordingly.
Posted by: B | Aug 10, 2009 7:46:28 PM
4 minutes, ... so less than I thought. Awesome.
Just walking to my car and I could get the current RDA... pretty cool!
26 in December, 17 in February
Good to know.
Posted by: Olwen Anderson | Aug 10, 2009 6:28:36 PM
Thanks Monica - I wonder if they've factored in the amount of body surface you need to expose to get the right dosage? Completely naked? Just hands and face?
My calcs for south eastern Australia at 8am came out as 7 minutes at this time of year.
