"Lactose intolerance is the inability to digest milk. Symptoms include abdominal pain, bloating, flatulence and nausea. It is estimated that 75% of adults worldwide show some decrease in lactase activity during adulthood ranging from 5% in northern Europe to more than 90% in some African and Asian countries." Wikipedia.
Looking after those special interest groups costs pennies but wins you fans. Lactose free dairy 'drink' to accompany tea and coffee - purchased from a local supermarket and as seen at a National Trust property courtesy of a supervisor who knows the issues.