Calcium and vitamin D3: Why calcium alone is often not enough

You take care of yourself and your diet, but is that alone enough for strong bones? The honest answer is: often not. Because calcium is a real team player. Partners such as vitamin D are essential for the mineral to get where it is needed [1].

In this article, we'll show you why this combination is so crucial, whether a dosage can quickly become too high, and how you can promote healthy bone metabolism with the right knowledge. Let's take a closer look together so you can understand what your body really needs.

Combining calcium and vitamin D3: An unbeatable duo

You may have asked yourself, “Why are calcium and vitamin D always mentioned in the same breath?” The answer lies in your body's physiology. You can think of it figuratively: Calcium is the building material for your bones. But without construction workers, the bricks just lie in front of the construction site.

The role of vitamin D3 as a door opener

Vitamin D3 is that construction worker. It acts as a key that opens the doors in your body. Without an adequate supply of this vitamin, your intestines have great difficulty absorbing calcium from food or supplements [2].

• Absorption in the intestine: Vitamin D controls the absorption of calcium from the chyme into the blood.
• Incorporation into the bones: It regulates the calcium level in the blood and sends signals that calcium should be incorporated into the bone structure.

If vitamin D is lacking, your body simply excretes the valuable calcium unused. Worse still, in order to keep blood calcium levels stable (which is vital for the heart and muscles), the body begins to release calcium from the bones when there is a deficiency [3]. This is exactly the opposite of what we want to achieve.

Why especially in old age and in winter?

Older people are particularly at risk here. The skin's ability to produce vitamin D through sunlight decreases with age [4]. Added to this is the modern lifestyle, where we spend a lot of time indoors. Vitamin D deficiency is therefore not uncommon in our latitudes. So if you want to support your bone health, the combination of calcium and vitamin D3 is almost a must.

Important to know: The German Nutrition Society (DGE) recommends a calcium intake of around 1000 mg per day for adults [5]. For vitamin D, the recommendation is 20 µg (800 IU) daily if the body is unable to produce it itself [6].

The “calcium paradox”: The role of vitamin K2

When discussing complex relationships, we must not forget a third player: vitamin K2. While vitamin D3 ensures that calcium enters the bloodstream, vitamin K2 acts as a navigation system.

Vitamin K2 directs traffic

There is a phenomenon whereby people have high levels of calcium in their blood but still develop brittle bones, while at the same time their blood vessels calcify. Vitamin K2 activates proteins (such as osteocalcin) that specifically incorporate calcium into bone tissue while keeping it out of the arteries and soft tissues [7].

1. Calcium provides the substance.

2. Vitamin D3 ensures its absorption into the blood.

3. Vitamin K2 ensures its incorporation into the bones (and protects the vessels).

For a holistic strategy, especially to support normal bones in old age, the trio of calcium, vitamin D3, and K2 is therefore often the most intelligent choice. You can find out more about the role of calcium and vitamin K2 here.

Intake and interactions: What promotes or inhibits absorption?

You pay attention to your calcium intake and perhaps even combine it with vitamin D3. But for calcium to be effective in the body, it must also be absorbed properly. This is where the environment in the gastrointestinal tract plays a crucial role.

What are the classic “calcium robbers”?

Certain food ingredients bind calcium in the intestine, making it unavailable. This does not mean that you have to avoid these foods, but you should combine them wisely [8]:

Oxalic acid: Found in spinach, rhubarb, Swiss chard, and cocoa. It forms poorly soluble complexes with calcium. Tip: Do not eat foods rich in oxalic acid at the same time as your main source of calcium.

Phytic acid: Found in cereal bran and legumes.

Phosphate: High amounts of phosphate (in sausage, processed cheese, cola, ready meals) can cause calcium to be released from the bones.

Salt (sodium): High salt consumption promotes the excretion of calcium via the kidneys. Those who eat a low-salt diet retain more calcium in the body.

Caffeine & alcohol: In large quantities, they promote calcium excretion.

What promotes absorption?

Acid: Stomach acid helps to dissolve calcium compounds. Therefore, it is often better to take calcium supplements with meals than on an empty stomach.

Vitamins D & K: As already described, they are essential for utilization.

Lactose: In people who tolerate lactose, milk sugar promotes calcium absorption.

FAQ: Frequently asked questions about use and combination

To give you even more confidence in using calcium and vitamin D, we answer the most frequently asked questions on the subject here.

Can calcium and vitamin D be taken together?

Yes, absolutely! Since they complement each other in their effects (synergistic effect), taking them together makes a lot of sense. Many dietary supplements therefore combine calcium and vitamin D3 directly. This makes it easier for you to remember everything.

When should calcium tablets be taken?

The best time to take calcium is usually with meals. Eating stimulates stomach acid production, which improves the solubility of calcium. In addition, many vitamin D supplements are fat-soluble. This means that they need some fat from food (e.g., oil in salad, yogurt, avocado) to be absorbed by the body. Tip: Since the body can only efficiently absorb a certain amount of calcium per meal (approx. 500 mg at a time), it makes sense to split the dose between morning and evening if you have higher requirements.

What should not be taken together with calcium?

Be careful with certain medications.

Thyroid hormones (L-thyroxine): Calcium can inhibit absorption. Allow at least 2 hours between taking these.

Antibiotics (e.g., tetracyclines): Here, too, complexes can form that weaken the effect of the antibiotic.

Iron: If you take iron supplements, try to take them at a different time from calcium to optimize the absorption of both minerals.

What are calcium and vitamin D3 good for?

This combination contributes to the following [5] [6] [9]:

• Maintenance of normal bones and teeth.
• Maintenance of normal muscle function.
• Vitamin D contributes to the normal function of the immune system.
• Vitamin D contributes to the normal absorption/utilization of calcium and phosphorus.
• For women aged 50 and over: Calcium and vitamin D help reduce the loss of bone minerals in women after menopause (low bone mineral content is a risk factor for osteoporotic bone fractures).

Is it possible to overdose on calcium and vitamin D3?

Yes, “the more, the better” does not apply here. An excessive intake of calcium (well over 1500–2000 mg daily) can lead to kidney stones or strain the blood vessels. A massive overdose of vitamin D is also harmful (hypercalcemia). Therefore, always adhere to the recommended amounts on the package or as agreed with your doctor. Dietary supplements should complement a balanced diet, not replace it.

The right team for your bones

Calcium is the foundation, but it is only in combination with vitamins D3 and K2 that it becomes a stable house. Instead of taking tablets indiscriminately, it is important to combine them wisely and understand your own needs. This will help your body to use calcium efficiently.

But that's not all there is to know about this exciting mineral. Discover more information and in-depth facts about calcium in our magazine so that you can take the best possible care of your bone health.

Sources:
[1] https://pmc.ncbi.nlm.nih.gov/PMC6954280
[2] https://pmc.ncbi.nlm.nih.gov/PMC3405161
[3] https://lpi.oregonstate.edu/calcium
[4] https://pmc.ncbi.nlm.nih.gov/PMC424123
[5] https://www.dge.de/calcium
[6] https://www.dge.de/vitamin-d
[7] https://pmc.ncbi.nlm.nih.gov/PMC8067793
[8] https://pmc.ncbi.nlm.nih.gov/PMC5804294
[9] https://www.usz.ch/Report-GERMANPRESS