Today I have been reading another medical book from the middle of the 20th century.
Diseases of Infancy and Childhood, by Wilfred Sheldon was first published in 1936 and went into at least six editions. Sheldon worked at Great Ormond Street and advised the government on child health.
The section I've been reading is on rickets, a deficiency disease caused by lack of Vitamin D that was common in the past and still crops up occasionally today.
Sheldon knew a thing or two about rickets and how it distorted every part of the growing skeleton in babies and toddlers.
He noted that rickets was more likely to occur in late winter. He was well aware that winter sunshine has no vitamin D generating effect in countries far from the equator. He also believed that food such as milk and eggs had less vitamin D in the winter, which seems very plausible.
He states that breastfed babies are less susceptible to rickets - presumably because many proprietary milks and foods in the past did not have added vitamin D. These days the babies most likely to get rickets are the breastfed babies of mothers whose bodies are low in vitamin D. This can be for dietary reasons (few animal fats) or because the mothers tend not to expose their skin to sunlight. These babies need vitamin D supplements to protect them.
There is a lot of research interest in vitamin D and the immune system these days. We know that there are receptors for the vitamin all over immune cells. You don't have a letterbox if you are not expecting mail.
So it was interesting that Sheldon says:
"Uncomplicated rickets is seldom a fatal condition: its danger lies in weakening the child's resistance to infection, the immediate cause of death being usually broncho-pneumonia or diarrhoea. The prognosis of fevers, particularly measles, whooping cough, and influenza, is made much worse when they are complicated by rickets."
If he was writing today he might have put it differently: a child with very low levels of vitamin D is more susceptible to infections - the function of their immune system is impaired.
There are only 3 ways to get vitamin D. By the action of sun on skin; by eating a diet rich in animal fats - oily fish being the richest source and by taking supplements.
We should wonder whether children today are getting the amount of vitamin D they need. Not much playing outdoors seems to go on and if they do go out on sunny days a layer of sunblock is often applied. Muslim girls do PE with their head, arms and legs covered. The many darker skinned children that live in places where sunshine is in short supply may also be vulnerable because darker skin makes vitamin D more slowly.
And older adults too. They may not spend much time sitting in the sun. Or if they do they are less likely to expose much flesh and older skin makes vitamin D more slowly than young skin.
We all need vitamin D. We don't know yet how much. We are just beginning to find out how it affects the immune system. A bit of sunshine on the skin, in moderation, is probably good for us. Sunburn is not.
I am not a fan of supplements generally. The only one I take, at least in winter, is vitamin D.