On Food and Cooking

other as yet unidentified substances. There
appear to be factors in tea and in onions
and parsley that slow bone deconstruction
significantly. Vitamin D is essential for the
efficient absorption of calcium from our
foods, and also influences bone building.
It’s added to milk, and other sources
include eggs, fish and shellfish, and our
own skin, where ultraviolet light from the
sun activates a precursor molecule.
The amount of calcium we have
available for bone building is importantly
affected by how much we excrete in our
urine. The more we lose, the more we have
to take in from our foods. Various aspects
of modern eating increase calcium
excretion and so boost our calcium
requirement. A high intake of salt is one,
and another is a high intake of animal
protein, the metabolism of whose sulfur-
containing amino acids acidifies our urine,
and pulls neutralizing calcium salts from