Q: "Is the food produced in glasshouses or hothouses deficient in vitamin D, due to lack of full sunshine? If not, where does the food get its vitamin D from?"
Suzan Kiemann, via email
A: Microbiologist and plant scientist Dr Robert Premier responds:
“Tricky question! While UV light is somewhat harmful to plants, recent work suggests that they do require it for some functions, including the formation of vitamin D. You’d have to assume that plants growing in hothouses receive some UV light otherwise they wouldn’t grow properly. Swedish research has also shown that even if plants don’t get enough UV light to produce their own vitamin D, they still produce provitamin D, a vitamin D precursor that forms at equivalent levels with or without exposure to UV light in plants. So whether conventionally grown or hothouse, it doesn’t matter.”