Vitamin D in Milk and Butter

A large number of studies have been made of the natural vitamin D content of milk. The factors affecting this content are reviewed by K. G. Weckel of the University of Wisconsin. In a study at the Michigan Agricultural Experiment Station, H. E. Bechtel and C. A. Hoppert found the vitamin D content of Guernsey milk to vary from 4.8 United States Pharmacopoeia units as a minimum during the winter months to 43.8 U. S. P. units a quart during summer months. Holstein milk was found to vary likewise from 3.1 to 27.7 U. S. P. units a quart. The vitamin D in the fat in the milk of both of these breeds varied from 0.11 to 0.9 U. S. P. units per gram. K. M. Henry and Dr. Kon obtained similar results for butterfat; and G. C. Wallis and T. M. Olson at the South Dakota State Agricultural Experiment Station obtained 8 or 9 U. S. P. units per quart for milk produced in November and April, but 32 U. S. P. units per quart for milk produced in July.

Wallis and Olson demonstrated that they could influence the vitamin D content of milk by variations in the vitamin D content of the diet. During stall feeding some of the vitamin D in milk is derived from the hays fed. The vitamin D content of milk has been increased by feeding COWS materials rich in vitamin D, such as cod-liver oil, irradiated yeast, and irradiated ergosterol. But studies with irradiated yeast, which has often been fed to improve the vitamin D in milk, indicate that only 2 or 3 percent of the vitamin D fed is recovered in the milk. Increasing the vitamin D content of the feed is, therefore, not an efficient method of improving the vitamin D potency of milk.

Kon and his co-workers demonstrated that the vitamin D potency of Milk from cows on winter rations may vary from 8.3 to 26.0 I. U. per kilogram and that from cows on pasture feed may vary from 5.3 to 17.0 I. U. per kilogram, depending in both cases upon whether the cows are kept indoors or are exposed to summer sunlight. They concluded that the vitamin D in summer milk is produced almost exclusively by the insolation of the cow; and efforts have been made to increase the vitamin D content of milk by irradiating the cow artificially with ultraviolet light. But this method also has not turned out to be effective for the purpose; and milk, as produced, is not an important source of vitamin D. Two methods are used commercially to increase the vitamin D content of market milks, namely the addition of vitamin D concentrates directly to the milk, or the direct irradiation of the milk itself with ultraviolet light. The former is now generally used; and most of the "vitamin D milk" on the market contains about 400 United States Pharmacopoeia units to the quart.

Vitamin C in Milk

As a result of the analysis of hundreds of samples of milk in various laboratories, the average vitamin C content of freshly drawn milk has been found to be close to'20 to 25 mg. per liter (approximately 1 quart)..

Paul F. Sharp, K. S. Guthrie, and D. B. Hand of Cornell state: "Actually there is, in the milk obtained each year from the cows of the United States, approximately as much vitamin C as is present in our entire citrus crop . . . If the vitamin C which is present in fresh milk were preserved, then 1 quart of milk would be equivalent to the juice of one orange so far as the amount of vitamin C is concerned."

The vitamin C content of fresh milk does not vary materially with the season or the feed, and varies little but possibly significantly in some cases with the breed of the cow. But the vitamin C in milk is unstable, urban consumers probably receiving not more than one-half to one-third of that originally present.

Vitamin C as purchased in capsules or tablets is fairly stable, but in milk, in the presence of riboflavin and dissolved oxygen, it is rapidly changed by the action of daylight to a form which, although still active as a source of vitamin C, readily undergoes still further oxidation even in the dark. Thus bottled milk may lose fully half of its vitamin C potency as a result of exposure to sunlight for half an hour.

Dr. Kon, who with M. H. Watson discovered this effect of light on the vitamin C in milk, suggests : "There are two ways of preventing loss of vitamin C from this cause. Exposure to light may be avoided. Cartons, for example, give a good degree of protection. Brown glass bottles would be ideal . . . As oxygen is needed for the reaction its removal from milk abolishes the action of light."

Vitamin C is also destroyed more or less in various methods of pasteurization; but, according to Aubrey P. Stewart, Jr., and Paul F. Sharp, of the Research Laboratory of Golden State Co., Ltd., San Francisco, "The causes for losses of vitamin C are shown to be the result of copper contamination and presence of dissolved oxygen, during pasteurization and especially on holding after pasteurization."

The vitamin C in milk fresh from the udder that is, that has not been exposed to light is said not to undergo destruction when pasteurized by holding at 145' to 150 F. for 30 minutes.

Stewart and Sharp recently made a study of the vitamin C content of 364 samples of pasteurized milk (237 in quart cartons and 127 in quart glass bottles) from consumers' homes and retail stores in the metropolitan area around San Francisco and Oakland, Calif. Because much of the milk was delivered during the afternoons, the samples were placed in a refrigerator at 10 C. and analyzed the next morning following the date of delivery. The average total vitamin C content of the samples was 5.8 mg. per liter; 110 samples that were held for another day in a household type of electric refrigerator at approximately 10 and were re-analyzed, showed a loss of 30 percent as a result of this additional day's storage.

Stewart and Sharp also determined the vitamin C content of 12 major brands (25 samples) of evaporated milk purchased in the retail stores of San Francisco and Oakland. The samples contained an average of 2 mg. of vitamin C per liter of reconstituted evaporated milk. They also analyzed 2,890 samples of spray-process dried whole milk that were only a few days old. These contained an average of 12.5 mg. of vitamin C per 125 g. powdered whole milk that is, in the amount of powder corresponding to 1 liter of whole milk; and samples of powdered whole milk that were stored at room temperature, air packed, retained 88.7, 85.5, and 79.7 percent of this vitamin C after 3, 6, and 12 months, respectively.

Apparently milk may or may not make a sizable contribution to human requirements for vitamin C, depending upon the conditions under which it is consumed and the way it has been handled or processed. When viewed in the light of the potency of the milk that the cow produces and the work that has been done on the control of factors affecting the loss of vitamin C in milk, one must agree with Sharp, Guthrie, and Hand when they said: "We can agree that the preservation of vitamin C in milk is important from the standpoint of the milk industry and of the nutrition of the nation."