Understanding the Past: Why Did They Start Putting Vitamin D in Milk?

October 20, 2025 •

4 min read

In the early 20th century, a debilitating bone disease called rickets was rampant in industrialized cities, affecting up to 80% of children in some areas. The public health initiative that emerged to combat this crisis explains the answer to the question: why did they start putting vitamin D in milk? The simple act of fortifying a common beverage became a powerful tool for disease prevention.

Quick Summary

The practice of fortifying milk with vitamin D began in the 1930s as a strategic public health campaign to eradicate the rickets epidemic caused by widespread vitamin D deficiency.

Key Points

Rickets Epidemic: In the early 1900s, a widespread vitamin D deficiency led to a public health crisis of rickets, a bone-softening disease, particularly affecting children in polluted cities.
Scientific Discovery: After the discovery of vitamin D in the 1920s, scientists realized that adding it to food could prevent rickets.
Milk as the Ideal Carrier: Milk was chosen for fortification because it was widely consumed by children and naturally contains calcium, a mineral that works with vitamin D to strengthen bones.
Successful Public Health Strategy: The large-scale fortification program initiated in the 1930s was highly effective, leading to the near eradication of nutritional rickets in many countries.
Continued Relevance: Fortification remains important today due to reduced sunlight exposure in modern lifestyles, which can lead to inadequate vitamin D levels.
Modern Health Benefits: Beyond bone health, adequate vitamin D intake from fortified milk and other sources supports immune function, cellular growth, and inflammation regulation.

The Widespread Scourge of Rickets

At the turn of the 20th century, rickets was a major health concern, particularly affecting children living in northern, industrial cities. The disease is caused by a severe deficiency of vitamin D and/or calcium, leading to soft and weakened bones. This resulted in painful deformities, most famously bowed legs, as the soft bones couldn't support a child's weight. Factors contributing to the epidemic included:

Lack of sunlight: Urban areas often had high levels of air pollution, which blocked the sun's ultraviolet B (UVB) rays. These rays are essential for the skin's natural production of vitamin D.
Inadequate diet: Dietary sources of vitamin D were scarce, especially for the poor. Many children lived indoors with limited sun exposure and diets lacking rich sources like cod liver oil.
Darker skin pigmentation: Individuals with darker skin require more sun exposure to produce the same amount of vitamin D, putting certain populations at a higher risk.

The Discovery and Early Eradication Efforts

American scientist E.V. McCollum is credited with discovering vitamin D in the early 1920s. He observed that cod liver oil could prevent and cure rickets in animal studies. This groundbreaking discovery, along with the recognition that sunlight exposure was also effective, paved the way for public health interventions. Early attempts at mass prevention were not always simple or effective. Some involved exposing children to UV lamps, while others tried fortifying milk by feeding cows irradiated yeast. These methods were inconsistent and difficult to implement on a broad scale.

Why Milk was the Answer

Milk proved to be the ideal and most effective vehicle for mass fortification for several reasons, making the solution both practical and widespread:

Ubiquity and Affordability: Milk was a staple, affordable food consumed widely across the population, especially by the target group of young children.
Nutritional Synergy: Milk is also rich in calcium, but without sufficient vitamin D, the body cannot absorb this calcium effectively. Adding vitamin D to milk created a powerful one-two punch for bone health.
Efficiency: By the 1940s, a more efficient method of adding concentrated vitamin D directly to the milk during processing was developed, replacing earlier, less reliable methods.

The Fortification Campaign and its Success

With a viable method identified, a public health campaign was initiated in the 1930s, gaining endorsements from prominent health organizations, including the American Medical Association. The result was a dramatic and rapid decline in the incidence of rickets. By the mid-20th century, the disease had been all but eradicated in developed countries with widespread fortification programs. This success story cemented food fortification as a key public health strategy for addressing widespread nutrient deficiencies.

Comparing Fortified Milk to Other Options


Feature	Fortified Cow's Milk	Unfortified Milk (e.g., Raw Milk)	Fortified Plant-Based Milk Alternatives
Vitamin D Content	Added vitamin D (usually D3), often at around 400 IU per quart.	Very low or negligible natural vitamin D content, though it varies slightly.	Added vitamin D (D2 or D3). Amount can vary by brand.
Calcium Content	Naturally high in calcium.	Naturally high in calcium.	Variable; many brands fortify with calcium, but amounts can differ.
Primary Function	Public health vehicle for widespread vitamin D and calcium intake.	A food source with natural vitamins and minerals, but without added health guarantees.	Dietary alternative to dairy, with added vitamins and minerals to match or exceed cow's milk.
Rickets Risk	Highly effective in preventing nutritional rickets.	High risk for deficiency in high-risk populations without other sources.	Effective in preventing rickets if consistently consumed and properly fortified.

The Ongoing Need for Fortification

While the initial goal of eradicating rickets was met, the relevance of vitamin D fortification persists today. Reduced sun exposure due to modern lifestyles, increased indoor time, and concerns about skin cancer risk mean many people don't get enough vitamin D naturally. This has led to a re-emergence of vitamin D deficiency as a global health concern, with some cases of rickets even reappearing.

The Importance of Consistent Intake

Ensuring adequate vitamin D levels is crucial for a variety of health functions beyond bone health. The vitamin plays a role in immune system support, cellular growth, and managing inflammation. For individuals who consume little to no milk, other fortified foods like some orange juices and cereals, or supplements, are necessary. Furthermore, specific populations, such as exclusively breastfed infants and individuals with darker skin pigmentation, need to pay special attention to their vitamin D intake.

Conclusion

Ultimately, the decision to start putting vitamin D in milk was a direct response to a preventable and devastating public health crisis. The fortification of milk was a simple, effective, and widespread solution that dramatically improved bone health for millions of children. Today, it remains an essential part of public nutrition policy, a testament to the power of targeted, food-based interventions. The continuing need for adequate vitamin D intake, both for bone health and wider systemic functions, means this historical intervention remains critically important in modern diets.

Frequently Asked Questions

Rickets is a bone disease in children caused by a severe deficiency of vitamin D and/or calcium. Vitamin D is essential for the body to properly absorb calcium and phosphorus, so a lack of it leads to soft, weak, and deformed bones.

Milk was chosen because it is a staple food that is widely consumed by children, who were the primary demographic affected by rickets. Its natural calcium content makes it an ideal carrier, as vitamin D enhances calcium absorption.

The practice of fortifying milk with vitamin D started in the United States in the 1930s as a public health initiative.

Unfortified or raw milk naturally contains only very small, insignificant amounts of vitamin D. The majority of vitamin D in milk today is added during processing.

For a time, milk fortification programs were highly successful and led to the near eradication of rickets in many developed nations. However, vitamin D deficiency has resurged, and some cases of rickets have unfortunately reappeared, emphasizing the continued need for vigilance.

In the United States, fortification of milk with vitamin D is not mandatory by federal law but is done voluntarily by most manufacturers. Some countries, like Canada and Finland, have made it a mandatory requirement.

Yes, in addition to dairy milk, many other food products are commonly fortified with vitamin D. These can include infant formula, certain brands of orange juice, cereals, and some plant-based milk alternatives.