I do not know if sunlight causes ink to fade faster when printed in books or in magazines. The best way to find out is to test it yourself! You can easily run an experiment where you expose a page of a book and a page of a magazine to sunlight for the same amount of time. Then, check to see which one has faded more.

I think many things can affect the answer. For example, the material that the ink is made of and the color of the ink probably matter. The temperature and humidity in the area probably matter, too. These factors will make it hard to say in general which will fade more.

It depends on the ink used to print them. The ink can bleach faster or slower in the sun, depending on what the ink is made from. Paper used to make sun prints bleaches the fastest. It's fun to put things on the paper, in the sun, to see the patterns the things make in a couple minutes.

You could leave an open magazine or book in the sun and see whether it bleaches after a day or more. Black ink should stay black in most cases.