Depends upon where you live. Above a certain latitude, there’s not enough UVB available, even in summertime, to activate the VitD in the body. Northern states typically.
So no matter how much you “go outside”, you won’t create enough Vit D internally and need to supplement. Your advice would be fine for CA-TX-FL latitudes, but not so good for WA-ND-WI-NY denizens.
There’s a lot more to it than just “going outside”.
Dr Holick: We did a study that showed that if you expose a person in a bathing suit to what we call 1 minimal erythemal dose, which is a light pinkness to the skin 24 hours after sun exposure, its equivalent to taking between 15 000 and 20 000 IU of vitamin D3. For a white adult, that would be equivalent to being exposed to sunlight in June at noon for about 10-15 minutes on a Cape Cod beach. Your body has a huge capacity to make vitamin D. Whats interesting is that the sunlight destroys any excess vitamin D that your body makes, so you could never become vitamin D intoxicated from sun exposure.
http://www.alternative-therapies.com/resources/web_pdfs/popular/0508_interview.pdf