Everyone has heard of vitamin D, but few really know how vitamin D works. For starters, did you know that our vitamin D primarily comes from our skin exposed to sunlight?
As the COVID-19 pandemic hits, many of us have been spending less time outdoors. As a result, we don’t get that lovely vitamin D as much as we used to. Vitamin D is essential for our health and well-being, and there are other ways we could supplement our vitamin D intake.
Importance of vitamin D for health
As a fat-soluble vitamin, vitamin D is important for a wide range of biological functions, such as:
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Increase absorption of calcium, which is essential for bone health and for preventing osteoporosis (brittle bone), thus reducing risk of bone fracture. Vitamin D deficiency can result in rickets in children and osteomalacia in adults.
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Increase muscle strength, which in turn helps to prevent falls among older people
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Keeping a healthy heart and blood vessels
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Lower risk of cardiovascular diseases such as strokes — Note: This is supported by the Health Professionals Follow-up Study , in which nearly 50,000 healthy men were followed for 10 years. It was found that those with lowest levels of vitamin D were twice as likely to have a heart attack as men who had the highest levels. However, taking vitamin D supplements has not been found to reduce cardiovascular risks, as demonstrated in this meta-analysis of 51 clinical trials.
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Lower risk of developing type 2 diabetes mellitus. Another study suggested that vitamin D may be beneficial for reducing risk of diabetes among those with vitamin D deficiency, whereas for those who already have normal levels of vitamin D to begin with, vitamin D supplementation does not seem to make much difference.
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Strengthen immunity against infectious disease such as flu and tuberculosis, as well as reduce risk of developing autoimmune diseases (immune system attacks its own body cells).
Sources of vitamin D
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The term vitamin D is, unfortunately, an imprecise term referring to one or more members of a group of steroid molecules (yes, vitamin D is actually a group of steroids!) Vitamin D3, also known as cholecalciferol, is produced when light energy is absorbed by a precursor molecule 7-dehydrocholesterol in our skin. However, the use of sunscreen products effectively blocks vitamin D production in the skin. In addition, the skin of those older than 70 years of age does not convert vitamin D as efficiently as in younger individuals.
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Besides the skin, we can also get vitamin D from our food, including egg yolk, fish oil and certain plants. The plant form of vitamin D is called vitamin D2 or ergosterol. However, natural diets typically do not contain adequate quantities of vitamin D. Hence, if you rarely get exposed to sunlight or consume food rich in vitamin D, vitamin D supplement may be necessary to prevent deficiencies.
Vitamin D2 v.s. Vitamin D3: what’s the difference?
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Vitamin D supplements in the market are available as Vitamin D2 and Vitamin D3. A meta-analysis of randomized controlled trials that compared the effects of vitamin D2 and D3 supplements on blood levels found that D3 supplements tended to raise blood concentrations of the vitamin more and sustained those levels longer than D2. So generally, vitamin D3 will be the preferred form of vitamin D as it is naturally produced in the body and found in most foods that naturally contain the vitamin. Nevertheless, if you only have access to Vitamin D2, it’s better than nothing at all.
Metabolism of vitamin D
Vitamin D, as either D3 or D2, does not have significant biological activity. Rather, it must be metabolized within the body to the hormonally-active form known as 1,25-dihydroxycholecalciferol, also known as calcitriol.
Such conversion of vitamin D into its active form requires the contribution of two organs: the liver and kidneys. This is why vitamin D and calcium deficiency is relatively common among individuals with kidney problems. People with kidney problems are usually prescribed with a calcitriol 0.25mcg once daily (Brand name: Osteocap®) to replenish the active vitamin D levels. An alternative to calcitriol is alfacalcidol (Brand name: One-Alpha, available in 0.25mcg and 1 mcg), in which the conversion into active vitamin D can be done in the liver, thus bypassing the kidney.
How much vitamin D should I take?
According to the Recommended Nutrient Intakes for Malaysia 2005, it is recommended that every individual aged below 65 years old has a vitamin D intake of at least 5 µg/day (80IU). Whereas for elderly aged 65 years old and above, the recommended intake is 15 µg/day (600IU).
Note: 1 microgram of vitamin D is equal to 40 IU (International Unit).
Toxicity
In general, all age groups should not exceed 50µg (2000IU) of vitamin D per day, and infants should not exceed 25µg/day (1000IU). Nonetheless, excessive exposure to sunlight does not lead to vitamin D toxicity, because the excessive heat and melanin production would reduce vitamin D3 production.
What’s dangerous is vitamin D over supplementation. Ingestion of excessive quantities of vitamin D over periods of weeks or months can be severely toxic to humans and animals due primarily to hypercalcemia (abnormally high levels of calcium). In fact, baits containing large quantities of vitamin D are used very effectively as rodenticides.
Who needs vitamin D supplementation?
The following groups are at risk of vitamin D deficiency and they might need dietary supplements to meet their vitamin D requirements:
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Breastfeed infants
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Elderly
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People with limited sun exposure
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Dark-skinned individuals
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People who are obese or have undergone gastric bypass surgery
Source: National Institutes of Health - Vitamin D: Fact Sheets for Health Professionals
We encourage you to consult a healthcare professional before purchasing any dietary supplements.
A word from Doc2Us
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References
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Dietary Reference Intakes for Calcium and Vitamin D - Overview of Vitamin D
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National Institutes of Health - Vitamin D: Fact Sheets for Health Professionals
Cover image credit: Photo by Diego PH on Unsplash
