Can sunshine alone provide us with optimal blood levels of vitamin D?

We all agree that sunshine alone can provide us with the Recommended Daily Allowance for vitamin D of 400 IU (that's 10 micrograms) per day. We all agree that solar ultraviolet radiation damages our skin and causes skin cancer. We all agree that exposure to sunshine is not necessary to receive the spectacular cancer-preventing benefit from vitamin D. (Several PubMed research studies claim that swallowing a 1,000 IU vitamin D pill each day would greatly reduce our risk of developing at least 17 different cancers). We all agree that exposure to sunshine is not necessary to receive the modest but certain bone-building and fracture-preventing benefit from vitamin D. So what don't we agree on? I found something. According to respected "get-much-more-uv-exposure" advocates such as Dr. Michael Holick and Dr. John McDougall, a few minutes of daily solar exposure would be all that you need to get all the vitamin D that you need: http://www.uvadvantage.org/ http://www.drmcdougall.com/misc/2005nl/may/050500pusunshine.htm http://www.drmcdougall.com/misc/2007nl/sep/vd.htm However, several research studies at PubMed would seem to dispute this claim. According to this first PubMed study, a person who avoided sunlight would need to swallow a vitamin D pill containing 12.3 micrograms (492 IU) of vitamin D each day to maintain a blood concentration of 25 nmol/L. A person who got plenty of sunshine would still need to swallow a vitamin D pill containing 7.2 micrograms (288 IU) of vitamin D each day to maintain a blood concentration of 25 nmol/L: http://www.ncbi.nlm.nih.gov/pubmed/19064513?ordinalpos=1&itool=EntrezSystem 2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery _RA&linkpos=3&log$=relatedarticles&logdbfrom=pubmed A second PubMed research study gives us similar numbers: http://www.ncbi.nlm.nih.gov/pubmed/19297462?ordinalpos=1&itool=EntrezSystem 2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery _RA&linkpos=1&log$=relatedarticles&logdbfrom=pubmed The Linus Pauling Institute at Oregon State University confirms that 400 IU of vitamin D is equivalent to 10 micrograms of vitamin D: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminD/ Of course, a blood vitamin D level of only 25 nmol/L is far less than the optimal blood vitamin D level of 95 nmol/L according to this third PubMed research study: http://www.ncbi.nlm.nih.gov/pubmed/16825677?ordinalpos=1&itool=EntrezSystem 2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery _RA&linkpos=3&log$=relatedreviews&logdbfrom=pubmed In the first 2 PubMed studies I mentioned, it would require a person who avoided sunlight to swallow a vitamin D pill containing 41.1 micrograms (1,644 IU) or 38.7 micrograms (1,548 IU), respectively, of vitamin D each day to maintain a blood concentration of 80 nmol/L. That's just short of the 95 nmol/L optimum blood vitamin D concentration claimed by the third PubMed research study I mentioned. To make a long story short, I don't think exposure to solar radiation is the healthiest way of getting our vitamin D (unless you don't know that vitamin D is good for you so you don't plan on buying vitamin D supplements). I personally am quite happy with the 2,000 IU vitamin D softgels that I purchased from Sam's Club at a very good price. Here's why I think sunlight is not the best way to get our vitamin D: (1)Despite what Dr. Holick and Dr. McDougall say, sunlight just can't give us enough vitamin D to get our blood concentration of vitamin D anywhere near the optimal levels. You'll still need to swallow a vitamin D supplement after your daily UV dose if you want to get your blood levels of vitamin D at or near optimum. (2)Increased risk of skin cancer, cataracts, damaged corneas, and damaged skin appearance. (3)Wasted time in the sun, increased risk of drowning, shark attacks, jellyfish stings, traffic accidents, mugging/rape, etc. (4)Sunlight is an unreliable UV source due to clouds and seasons. (5)Inexact dosage information makes it much more difficult to megadose accurately for those with severe osteoporosis. Will you choose to waste time and effort maintaining a log record of your daily dosage estimate based on your exposure time, age, skin complexion, latitude, season, clothing style, and cloud thickness?