As indicated above, you need to have a baseline test done to know what your level of Vit D actually is. For some of us who are REALLY low, prescription strength Vit. D is the only choice (I could not get enough sun to get my levels back to anything approaching normal). I take 50,000IU three times a week.
If your vitamin D level is normal or low normal, then things like certain types of lamps and actual sun exposure will help you keep it normal. However, if you are low, you could not consume enough food (even fortified products) to get it back in the normal range without prescription strength Vitamin D.
There are actually what you could think of as a few different forms of Vit. D. There is the product your body makes that lives in your skin and soaks up the sun and converts to Vitamin D. This is then used by your kidneys. Your body only makes a certain amount and the kidneys get first dibs. Any extra you make is converted to a different form and then goes toward all the other wonderful cells in your body.
The design of the body assumes periods of sun and periods of winter. Most people can get enough extra in the summer to tide them through winter in the northern hemisphere (and some can’t). While sunblock is a wonderful thing, it is contributing to the increase in people with really low Vitamin D levels.