Re: Sardines and vitamin D

Vitamin D is manufactured by animals, with the largest amounts being 
found in fatty fish and fish oils. Small amounts of Vitamin D are found 
in milk and most milk is fortified with added Vitamin D as are many bread 
and cereal products.  Vitamin D helps in the absorption of calcium, also 
found in sardines.  Thus for sardines it is a win-win; calcium and 
Vitamin D.  Vitamin D occurs at high levels naturally in sardines.  
Compared to vitamin fortified whole milk, sardines contain about 6X as 
much Vitamin D.  The best naturally occurring source of Vitamin D is 
fatty fish and fish oils, including sardines, salmon, mackerel and cod 
liver oil.
 

The most interesting thing is that herring, which is what is used in the 
United States for sardines, is not so much of a superior producer of 
Vitamin D but rather an accumulator of Vitamin D.  There are chemistry 
issues as to why herring have Vitamin D, but as to why herring are higher 
in Vitamin D: Fish synthesize Vitamin D, a steroid.  This compound is fat-
soluble and is not passed as a waste metabolite like some other 
vitamins.   So in fatty fish such as herring, salmon, mackerel the 
compound accumulates in fatty tissues.  

With thanks for much of the above text to Bruce Love of the Stinson 
Canning Company in Maine.