A Historical and Current Perspective
Milk has been described as nature’s most perfect food. It is an elixir of nutrients designed to nourish newborns and growing infants. So why mess with it? In the 1800’s to early 1900’s infantile rickets, a disease marked by improper bone development, was common in the inner cities where sunlight was lacking. It was considered the disease of “poverty and darkness.” The disease was treated with cod liver oil and later by exposure to sunshine. It wasn’t until the 1920’s that rickets was associated with deficiencies of vitamin D, a vitamin made in our skin when exposed to UV rays of sunshine. What followed was a gold star in dairy history. Messing with milk to increase its vitamin D content was considered instrumental in reducing the incidence of rickets (and a much better alternative to cod liver oil).
Vitamin D’s main role in human metabolism is in controlling levels of calcium in blood serum by stimulating calcium absorption in the GI tract and regulating calcium flux in the kidneys and bones. It is required for healthy bone development and maintenance; deficiencies result in rickets in growing children and osteomalacia (softening of bone through loss of Ca) in adults. With the exception of certain seafood, most foods, including milk, are poor sources of vitamin D. Vitamin D in whole unfortified 3.25% fat milk has been reported to range from 27 – 45 IU/qt. In a 1932 editorial in the Journal of the American Medical Association it was stated that “it ought to be of advantage if anti-rachitic properties (vitamin D) could be imparted … to a few foods that enjoy wide spread use … Milk is of particular interest because of its unrivaled content of calcium and phosphorous.” At this point, the American Dairy Industry was already in motion developing and applying methods to increase vitamin D levels in milk. The first method applied was “metabolized vitamin D milk,” developed in 1931, where cows were given feeds supplemented with irradiated yeast (precursor ergosterol converted to D2); levels of ~400 IU/qt of vitamin D2 were achieved, but this was at high costs and with low efficiencies (< 2%). In 1932 a method was developed to increase milk vitamin D3 content by exposing a thin film of milk to UV light, which converted a vitamin D precursor in milk to vitamin D3, similar to what occurs in the human skin. UV systems were able to provide milk with ~400 IU/qt of vitamin D3, but the milk often developed a “burnt” flavor (e.g., light oxidized; see October article). Milks directly fortified with vitamin D concentrates were also offered for sale at this time. Fortification was considered a superior method for increasing vitamin D levels in milk and is currently used today.
Regarding regulatory oversight, vitamin D milk was first defined in the 1939 USPH Milk Ordinance and Code (early editions of the Pasteurized Milk Ordinance, PMO); this was presented as an optional practice using methods and levels approved by the regulatory agency. In the 1953 Code, based on recommendations of the American Medical Association, 400 IU/qt vitamin D within Good Manufacturing Practices (GMPs; interpreted as 80 – 120%) was given as the target level if milk was fortified. This guidance continued in subsequent versions of the Code/PMO until the most recent version. In 1992, vitamin fortification levels were further clarified in a FDA memorandum (M-I-92-13) stating that levels should be 100 to 150% of label claims (i.e., 400 to 600 IU/qt). This memorandum, likely in response to an incident where eight people developed hypervitaminosis D from drinking milk from one dairy that was fortified at levels up to 500 times the target 400 IU/qt (~232,000 IU), also presented an upper level of 800 IU/qt that would be considered a potential public health hazard prohibiting further distribution.
Vitamin D at a level of 400 IU/qt currently stands as the target in the most recent edition of the PMO (2015) and in the current Code of Federal Regulations (CFR) standard of identity for milk (21 CFR 130.110). Vitamin D fortification of whole milk is still optional, but milks from which fat has been removed (e.g., nonfat, low fat milks) are required to be fortified, as vitamin D is removed as it is a fat soluble vitamin. Until recently 400 IU vitamin D was the Reference Daily Intake (RDI) or Daily Value (DV) but this has been increased to 800 IU with new nutritional labeling guidance. This increase in RDI/DV is based on the newer knowledge that higher levels are needed for proper calcium regulation and other functions of vitamin D, including potential roles in cell growth, differentiation and immunity and possible cancer prevention. Some in the medical community feel that vitamin D deficiencies are still a concern, especially with recommended avoidance of excessive sun exposure. With this increase in RDI/DV, the food additive regulation for vitamin D3 (21 CFR 172.380) was recently amended based on a petition from two dairy companies that allows additional vitamin D3 to be added to milk to a level not to exceed 800 IU/qt, if so desired. The standard of identity for milk (21 CFR 130.110) if fortified remains at 400 IU/qt of milk.
Vitamin D fortification of milk is one way to provide this needed nutrient to the public; most market milks are labeled as fortified. A number of past surveys have shown however that dairy processors do not always hit the mark, with under fortification most common, not only with vitamin D but with required vitamin A fortification of reduced fat milks as well (PMO states a 2000 IU/qt target; 2000 – 3000 IU qt GMP range; and 6000 IU upper limit). Developing standard operating procedures to ensure proper fortification levels is essential. Programs should consider:
- Vitamin concentrate supplier quality control
- conducting audits and periodic testing of concentrate potency for confirmation
- Vitamin concentrate receiving and storage
- check labels for proper fortification level as ordered; record lot numbers
- store product protected from light as recommended
- rotate stocks for first-in, first-out; use before expiration date
- Vitamin addition methods and locations
- concentrate added as directed (check labels & lot numbers each use)
- add ~10% over label; helps meet minimum levels without overages
- consider natural levels, especially vitamin A that varies more with fat level: ~1200 IU/qt for 3.25% fat milk; ~750 for 2% milk; ~375 for 1% milk
- continuous addition by positive displacement pumps (e.g., piston or peristaltic);
- add after standardization, before homogenization and pasteurization
- time pump speed to deliver correct amount based on product flow rate
- wire pump switch to only operate in forward flow and for product
- conduct daily calibration checks and routine maintenance
- place and inspect check valve at addition site
- manual addition by graduated cylinder to raw batch or balance tank
- measure known amount of vitamin concentrate for known volume of milk
- mix the entire volume of milk sufficiently after addition (in raw or pasteurized tanks) before packaging
- Vitamin reconciliation; performed daily
- check weight or volume of vitamin concentrate used and ensure that it matches volume of milk processed
- Vitamin testing
- test all product fat levels at least twice per year
- use a certified laboratory (e.g., under the Interstate Milk Shipment program)
- Maintain records for all activities including corrections and corrective actions
- concentrate added as directed (check labels & lot numbers each use)
Messing with nature’s perfect food can be a good thing; don’t mess it up.
FDA. 1992. M-I-92-13: Recommended levels of vitamins A & D in milk products.
FDA. 2015. Grade “A” Pasteurized Milk Ordinance. US Department of Health and Human Services, Public Health Service.
FDA. 2016. Food additives permitted for direct addition to food for human consumption; vitamin D2 and vitamin D3. Federal Register 81(137):46,578-46,582. July 18, 2016.
Fox and McSweeney. 1998. Chapter 6: Vitamins in Milk and Dairy Products. Pages 265-291 in Dairy Chemistry and Biochemistry. Blackie Academic & Professional.
Graulet et al. 2013. Chapter 10: Vitamins in Milk. Pages 200-219 in Milk and Dairy Products in Human Nutrition. Y. W. Park and G. F. W. Haenlein ed. Wiley-Blackwell.
Holick et al. 1992. The vitamin D content of fortified milk and infant formula. The New England J. of Med. 326:1178-1181.
Jacobus et al. 1992. Hypervitaminosis D associated with drinking milk. The New England J. of Med. 326(18):1173-1177.
Murphy et al. 2001. Fluid milk vitamin fortification compliance in NY State. J. Dairy Sci. 84:2813-2820.
Roadhouse and Henderson. 1950. Special Milk Products: Vitamin D Milk. Pages 433-449 in The Market Milk Industry. McGraw-Hill Book Co., NY, NY.