Of course, the sun is also free (unless you worry that 15 mins/day can cause cancer) while if you buy supplements you'd want the high quality ones and preferably in a fatty medium for easier absorption. The D3 form is more easily converted by the body into an active form.
It's important to qualify that this is only true of people with lower levels of melanin (ie white people). For Hispanics and Asians/Indians the number is probably closer to 60 minutes, and for those of African descent the number is closer to 120 minutes.
You're missing out, really.
:)
In the winter in the SF bay area, it's very unlikely your skin can make enough vitamin D.
After one winter here, I my D levels were at 20 ng/ml -- way below what many believe is the sufficient level of 30 ng/ml.
http://www.google.com/search?q=%223-6+times%22+%22vitamin+d%...
My battery is about to die in the iPhone, so I don't have time to curate the list, but from a quick glance a couple of the sources from the google search look credible.
The body was designed to get D from sun, and it is difficult to overdose that way unless you are a lifeguard. It is easy enough to overdose on D if it is taken orally.
There are other effects than vitamin D from sun exposure- it would be presumptuous to assume you could achieve optimal health from a vitamin D supplement.
In his book _The Vitamin D Solution_, Dr. Michael Holick ( the discoverer of the active form of Vit-D) debunks this myth with data. I haven't read most of it, but it looks interesting.
Excessive amounts of animal fat are bad since it is a saturated fat, but some is beneficial. I suspect that range fed beef has more vitamin D since animals in the open get more sun and would store vitamin D in a smaller amount of fat built up over more time.
Obese corn fed feed lot cattle are less healthy for other reasons also. The corn diet is very unnatural for them. It leads to rapid fat buildup with some meats containing over four times the fat of range fed animals. The diet causes the digestive system to become more acidic making the animals prone to various infections including E-coli a very dangerous bacteria. The E-coli mutates in the overly acidic animals becoming a form which humans often can't fight off without antibiotics if it wasn't already killed in cooking. The E-coli in range fed animals is not so troublesome. Bacterial that does survive in the animals loaded with antibiotics is also apt to be more resistant to treatment.
Because of the the danger of E-coli, ground beef must be cooked well done all the way through. Slaughter exposes meat from other parts of the animal to the bacteria and if gets mixed all the way through when ground. Other beef should be eaten fresh and washed well before cooking, and utensils and cutting boards used with the raw meat should be kept separate from those used for vegetables and other foods. Besides tasting better, non-ground beef is more nutritious if the color isn't cooked out. Meat that's still juicy contains a fair amount of iron in the blood.
PBS in the US has been running a documentary about corn production in Iowa. The subsidized inedible corn (tastes like cardboard, engineered for high yield per acre) is used mainly as cattle feed and to produce high fructose corn syrup, a non-nutritious addictive destructive AND CHEAP sweetener that's found its way into many of our foods. It's hurting us not only when consumed directly, but by degrading the beef produced as explained above. People consume more saturated fat in the beef. The excess fat and sugar has caused a major increase in diabetes in the last 20 years.
Although supplements help with vitamin D problems, we really should be looking closely at what we eat and how it is produced. END CORN SUBSIDIES!!! contact your representatives. The corn isn't profitable without subsidies, farmers (big business now) would switch to nutritious crops if not paid to do the wrong thing.
U.S. broadcasting has become dangerously consolidated in the hands of a small number of corporations and even more insidious venture capital groups. Pressure the F.C.C. and your representative for change, and watch and support your P.B.S. (non profit community tv) stations.
For all of us to be healthier we should step back and see what's going on, be educated, produce healthy foods, eat properly, and live a healthier lifestyle. Some would say that's all too costly, but disease treatment costs even more and there is no price tag on suffering.
http://latimesblogs.latimes.com/lanow/2009/10/california-agr...
Assuming equal carcinogenic potential from sun exposure and from such beds (which is most likely an incorrect assumption), the results should be insightful.
The absolute amount of Vitamin D needed is quite modest, and the risk of cancer is (typically seen as) proportional to sun exposure; hence the recommendation for some - but not much - UV exposure.