Chapter 9 – Minerals

9.2 Where Do Minerals in Foods Come From?

 Where Do Minerals in Our Diet Come From?

Have you ever wondered where the calcium in milk, the iron in spinach, or the fluoride in drinking water comes from? Unlike vitamins, which are produced by plants and animals, minerals cannot be made by  any  living organism. Instead, they have existed on Earth for millions of years, originating in rocks, soil, and water.   Understanding this journey helps explain why minerals are naturally present in so many different foods.

1.  Soil, Rocks, and Water 

Minerals naturally occur in rocks and the soil. As rocks slowly weather over thousands of years, they release minerals into the soil. Rainwater and groundwater dissolve many of these minerals and carry them into streams, lakes, oceans, and underground aquifers.

Examples include:

  • Calcium from limestone
  • Iron from iron-rich soils
  • Magnesium and potassium from rock minerals
  • Fluoride naturally dissolved in groundwater
    Water in a stream
    Figure 9.1 Water gets minerals from rocks. Photo by Elimende Inagella on Unsplash

2. Plants Absorb Minerals

Plants absorb dissolved minerals from the soil through their roots. Unlike vitamins, which plants can manufacture, minerals cannot be made by plants. Instead, plants take up minerals that naturally occur in the soil and water and store them in their roots, stems, leaves, fruits, and seeds. Farmers also add fertilizers to replace minerals removed from the soil and help crops grow. As a result, different plants become good sources of different minerals.

Examples include:

  • Corn absorbs phosphorus and potassium.
  • Spinach absorbs iron and magnesium.
  • Beans absorb zinc.
  • Potatoes absorb potassium.
Spinach growing on dirt.
Figure 9.2 Spinach absorbs minerals from soil and water. Photo by Veronica White as CC 2.0

3. Animals Obtain Minerals from Plants (or Other Animals)

Animals obtain minerals by eating plants, consuming other animals, drinking water, and, in some cases, mineral supplements or salt licks.These minerals are absorbed into the body and become part of the animal's bones, muscles, blood, milk, eggs, and other tissues. When humans eat animal foods, they receive many of these same essential minerals.

Examples include:

  • Cows transfer calcium from the plants they eat into their bones and milk.
  • Chickens obtain calcium from feed to produce eggshells.
  • Fish absorb iodine and other minerals from seawater and the organisms they eat.
  • Beef contains iron and zinc because cattle consume grains that contain these minerals.
    Kneeling cattle eating grass through a barbed wire fence.
    Figure 9.3 Cows consume minerals from the grass. Photo by James Rockwood at CC 2.0.

4. Humans Obtain Minerals from Foods and Beverages

When you eat plants or animals—or drink water—you receive minerals that originally came from the soil, rocks, and water. Because different foods provide different minerals, eating a wide variety of foods helps ensure you obtain all of the minerals your body needs for good health.

Some examples of how minerals get into our food supply are listed below.

Table 9.1  How Minerals Enter Our Food Supply
Mineral How Minerals Enter Our Foods
Calcium Limestone → soil → grass → cow → milk
Potassium Soil → potato or banana
Iron Soil → spinach or cattle
Magnesium Soil → nuts, beans, leafy greens
Zinc Soil → grains or meat
Fluoride Groundwater dissolves fluoride-containing rocks → drinking water → teeth
Iodine Ocean water → seafood, seaweed, or iodized salt

 

Common Questions About Minerals and Foods

Where Does the Calcium in Milk Come From?

Cows eat grasses and other plants that absorb calcium from the soil through their roots. After the cow digests these plants, the calcium is absorbed into its bloodstream and used to build and maintain strong bones and teeth. Some of the calcium is also transported to the mammary glands, where it becomes part of the milk produced to nourish the calf. When we drink milk or eat yogurt and cheese, we receive that same calcium, which originally came from the soil and was transferred through the grass to the cow.

Where does fluoride come from?

As groundwater flows through layers of rock, it dissolves small amounts of fluoride from the native rocks. As a result, some regions of the United States have naturally fluoridated groundwater, while others contain very little fluoride. Higher natural fluoride levels are common in parts of the Southwest and the Rocky Mountain states, whereas many areas of the Southeast, including Tennessee, have lower levels. [1]Drinking water that contains the recommended amount of fluoride helps strengthen tooth enamel, making teeth more resistant to decay. In communities where natural fluoride levels are too low, public water systems often adjust the fluoride concentration to the level recommended for good dental health.

Why is iodine added to salt?

Unlike calcium and potassium, iodine is often scarce in inland soils because much of the Earth's iodine is concentrated in the oceans. As a result, crops grown far from coastal areas may contain only small amounts of iodine. Before the 1920s, iodine deficiency and enlargement of the thyroid gland (goiter) were common in many inland regions of the United States, particularly around the Great Lakes and in the Appalachian Mountains.

In 1924, manufacturers began adding small amounts of iodine to table salt, creating iodized salt. This simple public health measure virtually eliminated iodine deficiency in much of the United States. Today, both iodized and non-iodized table salt are sold in grocery stores, so reading the label is important if iodized salt is your primary source of iodine.[2]

Specialty salts, such as Himalayan pink salt, sea salt, and kosher salt, are typically not iodized unless the package specifically states that iodine has been added. Although Himalayan salt contains trace amounts of naturally occurring minerals, including iodine, these amounts are too small and inconsistent to be considered a reliable source of this essential nutrient. Good dietary sources of iodine include seafood, dairy products, eggs, and foods prepared with iodized salt.[3]

Why are leafy greens rich in minerals?

Leafy greens such as spinach, kale, and collard greens are rich in minerals because their roots   absorb them from the soil, and their leaves store many of them. These minerals originate from weathered rocks and soil, but farmers may also add fertilizers to replace minerals removed during crop production. Fertilizers commonly supply nutrients such as potassium, magnesium, and other minerals needed for healthy plant growth. The leaves store many of these minerals, making vegetables such as spinach, kale, and collard greens excellent dietary sources of essential minerals.

Bioavailability of Minerals Varies

Minerals are generally absorbed less efficiently than vitamins, and many factors influence how much the body absorbs. Some plant compounds, including oxalates and phytates, reduce mineral absorption. In contrast, vitamin C enhances iron absorption, while vitamin D improves calcium and magnesium absorption. Aging and certain diseases can also reduce mineral absorption and increase the risk of deficiency.

DID YOU KNOW:   Not all fruits, vegetables, and dairy products contribute the same minerals—even when they look similar on your plate.

For example, milk and yogurt are rich in calcium and phosphorus, but cheese, derived from milk, has less. In contrast, bananas, potatoes, and spinach are standout sources of potassium, a mineral that plants use to regulate water balance—much like potassium helps regulate fluid balance in the human body. To sort the foods by mineral content, click the arrow in the header.

Food Calcium mg Phosphorus mg Potassium mg Magnesium mg Sodium mg
Milk, skim 1 c. 299 226 382 21 82
Soy milk, plain 1 c 299 69 187 61 84
Greek yogurt, 1 c 250 274 352 25 77
Cheese, cheddar 1 oz 149 97 16 6 135
Potato, baked 26 123 610 43 20
Banana, med. 6 26 422 31 1
Salmon, canned 3 oz 212 301 255 26 332
Chicken breast, 3 oz 21 182 332 22 50
Egg, boiled 25 86 63 57 62
Spinach, cooked 1/2 c 123 41 334 78 63
Beef, 3 oz 10 172 315 20 50
Apple, raw 12 19 186 9 2
Chia seeds, 1 oz 179 244 115 95 4
Almonds, 1 oz. 76 136 208 76 0.3

Review Questions

 

  1. U.S. Geological Survey. Fluoride occurrence in United States groundwater. Published May 11, 2020. Accessed July 8, 2026. USGS publication page ↵
  2. Leung AM, Braverman LE, Pearce EN. History of U.S. iodine fortification and supplementation. Nutrients. 2012;4(11):1740-1746. doi:10.3390/nu4111740 ↵
  3. Leung AM, Braverman LE, Pearce EN. History of U.S. iodine fortification and supplementation. Nutrients. 2012;4(11):1740-1746. doi:10.3390/nu4111740 ↵
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Introduction to Nutrition and Wellness, 2nd Edition Copyright © 2026 by Janet Colson and Sarah Harris is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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