Vitamin D (also referred to as “calciferol“) is a nutrient you need for good health. It is one of the four fat soluble vitamins (Vitamin A, D, E, and K), which are nutrients absorbed along with fats in the diet, and stored in the body’s fatty tissue and in the liver.

Vitamin D is necessary for the absorption of minerals (calcium, magnesium and phosphate), and it is also important for many other biological functions.

Apart from being present in a few foods and being available as a dietary supplement, Vitamin D is also produced endogenously when ultraviolet (UV) rays from sunlight strike the skin triggering vitamin D synthesis. The two most important forms of vitamin D in humans are  vitamin D3 (also known as colecalciferol) and D2 (also known as ergacalciferol). However, the form of vitamin D obtained from foods, supplements and sun exposure is pretty much useless in its actual form, as it is inert and must undergo an activation process that will turn the inactive form of calciferol in its active hormonal form called calcitriol.

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Why is vitamin D important?

Once activated, the vitamin D (calcitriol) circulates in the bloodstream as a hormone, playing a crucial role in homeostasis, calcium and phosphate metabolism, bone health, regulation of the immune system to fight off invading bacteria and viruses, neuromuscular functions, and reduction of inflammation.

To date, researches have shown that vitamin D can have a lot of health benefits. Studies have found links between low blood levels of vitamin D and increased risk of depression, multiple sclerosis, and osteoporosis. The latter happens when long-term shortages of vitamin D and calcium cause your bones to become fragile and break more easily.

Levels of vitamin D in the blood

To know whether you are getting enough vitamin D you need to have a blood test to measure a form of vitamin D known as 25-hydroxyvitamin D. This is measured in either nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL). One nmol/L is the same as 0.4 ng/mL.

Levels below 30 nmol/L (12 ng/mL) are too low and can be classified as a deficiency.

Levels of 50 nmol/L (20 ng/mL) or above are considered as being normal for most people.

Levels of 125 nmol/L (50 ng/mL) are too high and can be considered as being too high and hence they are toxic.

Not everybody is the same, and some people are more likely to struggle to get enough vitamin D. These include:

• Older adults;
• People who never go out in the sun;
• People with dark skin;
• People with conditions that limit fat absorption, such as Crohn’s disease, celiac disease and ulcerative colitis;
• Obese people or people who have undergone gastric bypass surgery;
• Pregnant women;
• Menopausal women;
• Breastfed infants;

What are consequences of too little vitamin D?

Too little vitamin D can lead to a bunch of health problems, these include:

• Serum reduction of calcium and phosphorus;
• Secondary hyperparathyroidism;
• Inappropriate mineralization of the bones (leading to rickets in children, and osteomalacia in adults);
• Muscular weakness;
• Abdominal pain;

What are consequences of too much vitamin D?

As anything in life, all the excesses can have a negative impact, and getting too much vitamin D is no exception to this rule, and it can be harmful.

Vitamin D blood levels (greater than 375 nmol/L or 150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, loss of appetite, weight loss and anorexia, hypercalcaemia (increased levels of calcium in the blood) and hypercalciuria (increased level of calcium in the urines), pain, soft tissue calcification, dehydration, kidney stone, and excessive urination and thirst. This can lead to kidney failure, irregular heartbeat, and even death!

You cannot get too much Vitamin D from sunlight because your skin limits the amount of Vitamin D it takes.

What are the sources of vitamin D?

As mentioned above, vitamin D is found in supplements and a few foods. These include:

• Fatty fish (mackerel, tuna, trout and salmon) and fish liver oils are the best source natural source of vitamin D;
• Beef liver, cheese, and egg yolks – provide small amounts of vitamin D;
• Mushrooms – minimal amounts of vitamin D;

In young and healthy adults, ten minutes of daily sun exposure is enough to get the amount of vitamin D that you need on a daily basis.

How much is the recommended dose of vitamin D?

The amount of vitamin D that you need daily depends on many factors (age, underlying medical conditions, etc.).

In the table below you can find the daily recommended amounts of vitamin D according to the age range. These are expressed in mg (micrograms) and IU (International Units).

1 UI = 0.025µg of calciferol

1µg of calciferol = 40 UI of vitamin D.

• 0 – 1 year = 10 µg (400 IU)
• 1 -70 years = 15 µg (600 IU)
• 71+ years = 20 µg (800 IU)
• Pregnant and breastfeeling teens and women = 15 µg (600 IU)

Can vitamin D interfere with other medications?

Vitamin D can indeed interact with some medications:

• Steroids such as prednisone – can lower your blood levels of vitamin D;
• Orlistat is a weight loss medication – It can reduce the amount of calciferol your body absorbs from food and supplements;
• Cholesterol-lowering statins such as atorvastatin, simvastatin etc., might not work as well if you take a high dose of vitamin D supplements.
• Thiazide diuretics could raise your blood calcium level too high if you take vitamin D supplements.

Take-home points

• Vitamin D (calciferol) is an important nutrient that we need in order to have a good bone health, metabolism, immune system and overall health;
• Vitamin D can be found in certain foods, supplements and it is also produced by the body when the ultraviolet rays strike the skin;
• Optimum levels of vitamin D vary between different age groups and its absorption can be affected by many factors;
• Low levels and high levels of vitamin D can cause serious health problems;
• In normal circumstances, you can get your optimal amount of vitamin D with 10 minutes daily sun exposure.