Recently a friend of mine told me that caffeine together with milk can create some carcinogenic compound. I haven't heard about it so far, neither found an article about it on google. Is there any possibility that this is true?
Milk doesn't affect caffeine effects. Adding milk can affect the time in which your body absorbs caffeine, it is extended, but you won't probably feel this. In 1997, scientists discovered that your nervous system won't be as stimulated (compared to drinking dark coffee) when you'll drink coffee with milk, but there won't be much of a difference in the concentration of caffeine in your blood. There's no confirmation that milk reacts with caffeine and affects it in any way, but there's a thing with which milk does interact. It's called CGA, chlorogenic acid, a highly active polyphenol with glycolytic and insulin-sensitizing properties and, of course, antioxidant and anti-inflammatory properties. Adding milk to coffee can lower the bioavailability of chlorogenic acid and other polyphenols by binding them to milk proteins, especially beta-lactoglobulin. You won't feel the difference so much, you'd have to look at numbers on your blood test to tell that there's something different apart from the taste of the coffee. Nothing's gonna be a problem unless you don't have moderation on how much you drink it.