Queen Elizabeth II drank the same tea, the same way, for more than seventy years. Earl Grey, loose leaf, a splash of milk, no sugar, and properly hot — her former chef Darren McGrady, who cooked for her for eleven years, has described it in interviews.

In 2003, a team at Brigham and Women's Hospital and Harvard Medical School published a study in PNAS on what black tea does to the immune system. Twenty-one volunteers. Eleven drank five to six cups of black tea a day; ten drank instant coffee. Blood tested at two weeks and four.

The tea drinkers' gamma delta T cells — the immune system's first responders — came out swinging. The coffee drinkers' didn't.

But twenty-one people is a very small study. Nobody in it caught fewer colds, because illness was never measured. The lead researcher said himself it needed repeating in more people, and in the twenty years since, it never has been at scale.

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