The Science Behind Vitamin D Supplements

Jessica Clifton

by Jessica Clifton

8th April 2020

Vitamin D is important in the process of calcium absorption by the bones. It also has an important role in immunity and neurological functions. A deficiency in vitamin D can cause loss of bone density, which eventually can lead to osteoporosis. Severe vitamin D deficiency also causes osteomalacia or softening of the bones, symptoms of which include bone weakness, bone pain and weakness of the muscle.

The science behind vitamin D supplements can explain how diseases develop because of vitamin D deficiency, how they can be treated or prevented, and the exceptions when not to take supplements.

What are the sources of vitamin D?

Vitamin D is produced by our skin when we are exposed to UV light – simply by going outside on a sunny day, for example. Of course, it is best to go out in the early morning when UV radiation isn’t so strong that it burns the skin. You can also get vitamin D from the following food sources:

  • Cheese
  • Egg yolks
  • Fatty fish, like tuna, mackerel, and salmon
  • Foods with added vitamin D, for example, dairy products and cereals

In some cases, however, you may consider taking vitamin D supplements (but you should first consult your doctor to see if you really need this supplement).

When should you not take vitamin D supplements?

Since vitamin D is fat-soluble and it aids in the absorption of calcium, it can accumulate and become toxic. It may lead to calcium build-up in your blood, a condition known as hypercalcemia. The kidney can be affected as calcium stones may form.

You should not take vitamin D supplements if you have the following conditions:

  • Sarcoidosis (an inflammatory disease that affects the lungs and lymph)
  • High amounts of phosphate in the blood
  • High amounts of calcium in the blood
  • An excessive amount of vitamin D
  • Arteriosclerosis obliterans (arterial blockage)
  • Kidney stones
  • Reduction in kidney function

What are vitamin D supplements?

You can find vitamin D  naturally in food or as pharmaceutical supplements. Supplements are typically in gel pill form, and it’s necessary to take a specific dosage.

Vitamin D supplements often come in gel pill form

Vitamin D supplements often come in gel pill form

 Four forms of vitamin D exist, but only two have important roles in our body. The two main forms of vitamin D are the following:

  • Vitamin D2 – known as ergocalciferol and is commonly found in vegetables
  • Vitamin D3 – cholecalciferol, commonly found in animal sources

Most physicians recommend taking vitamin D3 supplements since this is the vitamin most active in the body. Vitamin D2 is simply metabolised by the liver into vitamin D3 for it to be useful.

Physicians typically prescribe vitamin D supplements to those who have certain ailments that are caused by deficiency in vitamin D. People who are suffering from hypoparathyroidism, for example, are usually prescribed with vitamin D supplements. Those who suffer from this condition have very low calcium in their blood. This calcium deficiency causes muscle cramps and spasms, body weakness, and general fatigue.

Symptoms of vitamin D deficiency

Some people are more at risk of vitamin D deficiency than others. The following people have a higher risk of being deficient in vitamin D:

  • Breastfed infants
  • The elderly 
  • Pregnant women
  • Obese or overweight people
  • People with osteoporosis, kidney disease, or liver disease
  • People who take certain medicines such as cholestyramine, anti-seizure drugs, glucocorticoids, and antifungal drugs

What is the chemical formula of vitamin D?

The two main forms of vitamin D differ only by one carbon atom. Vitamin D3 is biochemically more active in the body than vitamin D2. Generally, vitamin D is a secosteroid (a type of steroid) that is biosynthesised in the skin when ultraviolet rays, typically from sunlight, degrade a type of cholesterol in the skin known as 7-dehydrocholesterol.

The chemical formula of vitamin D - C27H44O3

The chemical formula of vitamin D

The respective chemical formulas of the two main vitamin D forms are as follow:

  • Vitamin D2 (ergocalciferol) – C28H44O2
  • Vitamin D3 (cholecalciferol) – C27H44O3

The other forms of vitamin D are the following:

  • Vitamin D1 – a one-is-to-one mixture of ergocalciferol with lumisterol
  • Vitamin D4 – also known as 22-dihydroergocalciferol, with the chemical formula C28H46O4
  • Vitamin D5 – sitocalciferol, with the chemical formula C29H48O5

Do vitamin D supplements work?

Taking vitamin D supplements does not necessarily need a prescription. Normally, a healthy person only needs about 600 to 700 IU of vitamin D per day. Without a prescription, supplements should not exceed 4,000 IU per day. IU stands for International Unit and is the measurement of fat-soluble vitamins.

One IU is equivalent to 0.025 mcg (micrograms), making the limit for vitamin D equal to 4,000 IU/day x 0.025 mcg/IU = 100 micrograms or 0.1 milligrams. This the upper safe limit for healthy adults.

Vitamin D supplements work best for those who have illnesses arising from a deficiency in this vitamin. It does not have any additional benefit when taken by a healthy person. It may only lead to health risks when taken in excess of the upper safety limit.

Health benefits of vitamin D

The health benefits of having a normal amount of vitamin D in your body

To be safe, it is still best to consult your doctor before taking any supplements. You could also naturally include more vitamin D in your diet. These are some food sources of vitamin D and the corresponding IU:

  • Salmon, pink, cooked, 3 ounces – 444 IU
  • Tuna fish, canned in oil, drained, 3 ounces – 229 IU
  • Sardines, canned in oil, drained, 3 ounces – 165 IU
  • Milk, non-fat, fortified, 8 ounces – 116 IU
  • Orange juice, fortified, 8 ounces – 100 IU

How long do vitamin D supplements take to work?

Just like other fat-soluble vitamins like vitamin A and vitamin E, vitamin D does not dissolve in water. It is best absorbed in the bloodstream if you take it along with high-fat food like avocados, nuts, eggs, and full-fat dairy products.

In one study that involved 50 older adult participants, it was found that taking vitamin D supplements alongside fatty meals increased the levels of the vitamin in the blood by 32% in a period of twelve hours compared to taking the supplement with a low-fat or fat-free meal.

The efficacy of vitamin D supplements is directly proportional to the amount that is absorbed in the bloodstream and ultimately by the body’s cells, particularly the osteogenic cells or bone cells. Depending on the ailment and dosage, it may take days or even up to several months before the full benefit of the supplements is apparent.

What are vitamin D supplement side effects?

As previously mentioned, vitamin D supplements have an upper limit of safety level for most people. This may vary depending on health conditions. If you overdose on the supplements, toxicity may build up in your body. The main side-effect is excessive absorption of calcium in the bloodstream.

Other side-effects of taking too much vitamin D can be:

  • Formation of kidney stones
  • Disorientation
  • Muscle weakness
  • Bone pain
  • Poor appetite and possible weight loss
  • Extreme thirst
  • Frequent urination
  • Nausea, vomiting, or constipation
  • Fatigue

The science behind vitamin D supplements is clear that it should be taken with caution. Unlike water-soluble vitamins, this supplement can accumulate and become toxic. Consulting a physician before taking any supplement is essential. 


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