Purity Milk is suitable for Sikhs.
Sevadars contacted Purity on November 25, 2008 and here is their response:
Vitamin D3 is formed naturally in human skin where 7-dehydrocholesterol, a steroid alcohol, is irradiated by sunlight and assimilated slowly into the body. It is converted to its active form (1,25-dihydroxycholecalciferol) in the kidney and released into the bloodstream. Vitamin D3 is produced commercially by irradiating 7-dehydrocholesterol, the same found in human skin, only commercially it is extracted from lanolin. When ingested by humans, the synthetic D3 is also converted to its active form in the kidney. Although lanolin is obtained by sheep, Vitamin D3 is considered Kosher and Pareve because the sheep are not slaughtered to obtain the wool, from which lanolin is extracted.
Vitamin A is a fat soluble, long chain alcohol which occurs in nature only in the animal organism. Vitamin A precursors (provitamins), widely distributed in the vegetable kingdom as carotenoid, can be transformed within the intestinal wall into Vitamin A. Vitamin A in an esterified form is preferred for nutritional use. Vitamin A is produced commercially by reacting calcium carbonate with water until twenty carbon atoms are connected to a water molecule. This is the alcohol, Vitamin A, which is esterified with palmitic acid to form the ester, Vitamin A Palmitate.
Vitamin A Palmitate is considered Kosher and Pareve.