Imagine life in the early 1900s.

At that time, nearly 80% of the children in Boston had rickets, a condition that leads to the softening and weakening of bones.

We know now that rickets is related to a deficiency of calcium or vitamin D and generally affects children.

Vitamin D helps with absorption of calcium and phosphorus from food. Consequently, a lack of vitamin D makes it difficult to maintain adequate levels of those elements in bones, leading to rickets.

Rickets became widespread during the Industrial Revolution’s increase in child labor. Children working in factories did not have much exposure to sunlight, and factory pollution blocked much of the sunlight if they were outdoors.

Vitamin D is unique in that it can be synthesized in the skin with exposure to sunlight. It does not occur naturally in many foods beyond fatty fish — tuna, swordfish, salmon — and even eating recommended amounts of the right fish does not provide enough of the vitamin in a week to help with the problem, according to the National Institutes of Health.

In addition to weakened bones, symptoms of rickets include stunted growth, delayed motor skills, pain, muscle weakness and skeletal deformities.

By 1919, scientists were studying the cause of rickets, experimenting with different diets fed to puppies.

The puppies were fed only bread and low-fat milk, inducing rickets, and then were treated with two specific diets. One consisted of yeast (for vitamin B) and orange juice (for vitamin C), and the other cod liver oil and butterfat.

The diet with added vitamins B and C did not reduce the rickets symptoms, but the diet containing what was later named vitamin D did.

Voluntary addition of vitamin D to milk by processing plants began in the 1930s and is a practice continued today.

However, there was some carelessness among some processors during World War II that led to vitamin D overdoses in infants and young children.

For a while, many European countries banned the addition of vitamin D to milk. Once the problem was recognized, it was quickly corrected.

The number of rickets cases in Boston decreased to nearly zero after milk fortification became common practice.

Fortified Milk

Vitamin D was originally added to milk by irradiation or feeding cows irradiated yeast. A simpler and more effective method — adding vitamin D concentrate to milk — was developed and put into use in the 1940s. This method is still in practice today.

Unfortified milk can be sold in the U.S., but it must be labeled as such.

If you are anti-dairy, you might argue that vitamin D can be supplemented in ways that do not include drinking milk.

You might be right, but milk is readily available, relatively inexpensive, and wholesome in many other ways for children.

The greatest value of milk fortified with vitamin D lies in its ability to increase the absorption of calcium, which occurs naturally in milk, through the small intestine.

Calcium is required by the body, not only for the mineralization of bones, but also for neuromuscular function.

So, as one Washington Post journalist has said, “Humans are kinda capable of photosynthesis.” And they use the sun to produce what scientists have long believed to be the oldest hormone on Earth — vitamin D.

OK, it isn’t actually photosynthesis in the way plants do it to produce food, but it has the same basic outcome — using sunlight to synthesize a chemical.

We can ensure that our children, and we as adults, have sufficient vitamin D by drinking wholesome, fortified milk, plenty of which is available throughout the commonwealth.

The Pennsylvania Milk Marketing Board is always available to respond to question and concerns. I can be reached at 717-210-8244 or by email at

Lancaster Farming

Carol Hardbarger is the secretary of the Pennsylvania Milk Marketing Board.


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