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Does calcium turn yellow?

Calcium is an important mineral that plays a vital role in many of the body’s functions. It is found abundantly in dairy products, green leafy vegetables, nuts, and fortified foods. But does calcium actually change color over time? Can calcium turn yellow? Let’s take a closer look at the science behind calcium and find out if and why it may change color.

The Role of Calcium in the Body

Calcium is crucial for building and maintaining strong bones and teeth. It also supports proper muscle, nerve, and cardiovascular function. The body tightly regulates calcium levels in the blood, and if there is not enough calcium obtained through the diet, the body will leach calcium from the bones to maintain normal blood calcium levels. That’s why getting enough calcium is important for bone health.

Here are some of the key functions of calcium in the body:

  • Forms the mineral portion of bones and teeth
  • Supports bone remodeling and repair
  • Essential for muscle contraction
  • Helps blood clot
  • Aids in nerve transmission
  • Regulates heart rhythm

Without adequate calcium, the risk of developing osteoporosis and fractures increases significantly. That’s why daily calcium intake recommendations have been established.

Recommended Calcium Intake

The recommended dietary allowance (RDA) for calcium is as follows:

Age Calcium RDA
0-6 months 200 mg/day
6-12 months 260 mg/day
1-3 years 700 mg/day
4-8 years 1,000 mg/day
9-13 years 1,300 mg/day
14-18 years 1,300 mg/day
19-50 years 1,000 mg/day
51-70 years 1,000 mg/day
> 70 years 1,200 mg/day

As you can see, calcium needs change over a person’s lifespan. The main groups at highest risk of low calcium are children, adolescents, and older adults.

What Is the Chemical Structure of Calcium?

Now that we’ve reviewed why calcium is so important, what exactly is it? Here’s a look at the chemical structure of calcium:

  • Atomic number: 20
  • Atomic symbol: Ca
  • Atomic weight: 40.078
  • Density: 1.55 g/cm3
  • Melting point: 842°C
  • Boiling point: 1484°C

Calcium is considered an alkaline earth metal. When pure, it is a dull gray metal. The calcium used in supplements and added to foods, however, is typically a calcium compound such as calcium carbonate, calcium citrate, calcium lactate, or calcium gluconate.

Common Calcium Compounds

Here are some of the common calcium supplements and compounds added to foods:

Compound Description
Calcium carbonate Most common calcium supplement
Calcium citrate More easily absorbed, especially for people with low stomach acid
Calcium lactate Added to foods and has high bioavailability
Calcium gluconate Used in calcium-fortified orange juice
Calcium phosphate Found naturally in dairy foods

The amount of elemental calcium varies in each compound. For example, calcium carbonate is 40% elemental calcium, while calcium citrate is 21% elemental calcium.

Does Calcium Change Color?

Now back to the original question – does calcium turn yellow over time? The short answer is yes, calcium compounds can gradually change color, especially if exposed to air and/or light.

Here’s a more in-depth look at why calcium may turn yellow:


One of the main reasons calcium supplements or foods fortified with calcium can change color is oxidation. Oxidation occurs when calcium compounds are exposed to oxygen in the air. This causes a chemical reaction that leads to small changes in the molecular structure, which alters the color.

Calcium carbonate is one of the calcium compounds most susceptible to oxidation. Over time, the normally white powder can take on a yellow, tan, or even grayish hue due to oxidation.

pH Levels

Changes in pH can also cause calcium compounds to change color. Calcium carbonate, for example, forms a white solid powder in its pure, neutral form. But when exposed to acidic conditions, the normally white calcium carbonate can take on a yellow or brownish appearance. The more acidic the environment, the more pronounced the color change.


Another potential reason for color changes in calcium is contamination with trace impurities, such as iron or magnesium. These metals can react with calcium compounds, leading to subtle color changes over time, especially in supplements or fortified foods that contain calcium salts like calcium carbonate or calcium phosphate.

Light Exposure

Exposure to light, especially ultraviolet light, can also degrade calcium compounds and cause discoloration. That’s why many calcium supplements come in opaque, light-blocking containers to help prevent light-induced color changes.

Is Yellow Calcium Still Safe?

Now that we know why calcium can turn yellow, is it still safe to take? In most cases, yes – a yellowish tint does not make calcium dangerous or toxic.

Here are a few key points on safety:

  • Oxidation does not significantly degrade calcium’s nutritional value, though highly oxidized powders may have reduced bioavailability.
  • Color changes due to pH do not necessarily impact safety. However, extremely acidic products with a lot of discoloration may have lowered potency.
  • Contamination with small amounts of impurities like iron are not harmful, though heavily contaminated supplements should be avoided.
  • Light exposure reduces potency over time, but does not make calcium unsafe to take.

The FDA does set limits on heavy metal contamination in supplements like calcium. As long as these limits are met, discoloration itself does not indicate a safety issue.

That being said, major color changes, foul odors, or other signs of oxidation and degradation mean the supplement may have reduced efficacy and it’s a good idea to replace it.

Tips for Preventing Discoloration

Here are some tips for keeping your calcium supplements and fortified foods from changing color:

  • Purchase calcium supplements in opaque containers and store away from light.
  • Avoid buying calcium powders or tablets that are already yellowed.
  • Check expiration dates and don’t use calcium that is expired.
  • Store calcium in a cool, dry place.
  • Don’t buy more calcium than you can use within the expiration timeframe.
  • Be aware that multivitamins with calcium tend to yellow faster than calcium-only formulas.

The Bottom Line

While pure calcium is a dull gray metal, the calcium found in supplements and foods is typically a white powder in its natural state. However, over time, calcium carbonate, calcium phosphate, and other calcium compounds can undergo oxidation and pH changes that cause discoloration.

A yellowish tinge is common in older calcium supplements but does not necessarily impact safety or efficacy. However, major color changes, foul odors, and signs of extensive degradation indicate the calcium is oxidized and potentially less potent. To help prevent discoloration, store calcium properly away from air, heat, light, and humidity.

As long as it has been stored correctly before the expiry date, yellowed calcium is generally safe to take. But for best results, it’s wise to replace heavily discolored supplements with a new bottle.

With its multitude of vital functions, getting enough calcium is important at all stages of life. Being aware of how it can degrade over time allows you to optimize its stability and ensure you are meeting your daily calcium needs for strong, healthy bones and body.