Can we synthesize D with sunblock on? Doctors these days recommend NO unprotected sun exposure.
How much sun exposure is required for our daily dose of Vitamin D? If I take a 30 minute walk outside every day is that sufficient or do I still have to supplement?
How much skin has to be available to the sun to do the job?
I always wear sunblock on my face, and at this time of year (in upstate NY) that's the only skin that sees sunshine.
The rest is sunblocked, windblocked, coldblocked, snowblocked with multiple layers of clothing!
-- Jennifer Armstrong
Saratoga Springs, NY
We are unable to synthesize vitamin D with sunblock on because all products on the market act as barriers against either solely UVB rays or, if advertised as "full spectrum," both UVA and UVB rays.
Remember -- only UVB rays are associated with Vitamin D synthesis.
From an exposure standpoint, all you need is 10 minutes a day, three days a week, when the sun is at its highest point in the sky.
Even though these 10 minutes are without sunblock, it is believed that the benefits of adequate vitamin D levels outweigh the risks of soaking up sunrays without protection for such a short amount of time.
That said, people who live north of Florida -- like you, Jennifer -- must supplement from October to March, as the sun is too low in the sky for its UVB rays to penetrate the atmosphere.
Although current Vitamin D Daily Values for adults are set at 400 International Units, it is becoming increasingly clear that people should be supplementing with approximately 800 IUs a day.
Since the elderly and darker-skinned individuals synthesize lower amounts of this vitamin from the sun, it is recommended they supplement even during Summer months so as to not expose their unprotected skin to the sun for longer amounts of time.