The D vitamins are fat-soluble vitamins that play an important role in immune function (see my previous blog), calcium absorption, bone health, cognitive function, reduce risk of various cancers, protect against Alzheimer’s and helps in the assimilation of vitamin A (1,2).
Despite of its vital role to our health, many of us are deficient in vitamin D. Some more than others.
Vitamin D Production
Vitamin D is produced in our body with the help of sunlight and it also may be supplemented by vitamin D pills. Our skin produces vitamin D when exposed to sunlight, but due to the skin cancer risk, many people avoid sun exposure or use sunscreen, which prevents the body from producing vitamin D. By the way, approximately 10 minutes of sun exposure is typically sufficient for your daily vitamin D dose. Also, after a suntan is established, vitamin D production through the skin stops.
There are two forms of vitamin D dietary supplements: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). It is important to understand their differences when choosing which vitamin D supplement to take.
When you ask for a vitamin D in the store, the attendant will likely give you the D2. This is because these two terms are commonly used interchangeably. As their actual names suggest, D2 and D3 vitamins are different from each other.
Sources of Vitamin D’s
First, vitamin D2 comes from plant sources, such as wild mushrooms, as well as fortified foods, such as milk or cereal products. Vitamin D3 mainly comes from animal sources such as fish oil, fatty fish, liver, and egg yolks. When your skin is exposed to sunlight, it produces vitamin D3. For this reason, vitamin D3 is sometimes referred to as the sunshine vitamin.
Other than the sunlight source for vitamin D3, vegans and vegetarians are limited to the supplemental form vitamin D2 only.
Which vitamin D Is More Effective?
Vitamin D2 and D3 are absorbed into the bloodstream where they are metabolized by the liver into 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3, or collectively known as 25D or calcifediol. Calcifediol is the vitamin D complex circulating in your blood, and its levels directly reflect your body’s stores of vitamin D. Calcifediol is commonly referred to as the bio-active form of vitamin D. When your doctor orders lab tests to check your vitamin D levels, they are measuring your calcifediol (25D) levels.
There have been several studies comparing whether supplementation with vitamin D2 or D3 produces a higher blood level of calcifediol. A study (3) published by the National Institutes of Health was conducted in elderly, post-menopausal women who had been identified as vitamin D deficient. It compared the effects of receiving a single high dose of vitamin D2 or vitamin D3 on calcifediol levels. The study concluded that vitamin D3 produced about twice the amount of circulating calcifediol in this patient population versus that of vitamin D2.
In a separate clinical trial (4) comparing a 10-week regimen of twice weekly 50,000 IU dosing of both vitamin D2 and vitamin D3 in demographically matched groups, vitamin D3 was also found to be superior in producing higher levels of 25D, or calcifediol.
In terms of the lab tests which measure vitamin D levels, your doctor may evaluate total 25D or free 25D, or both. These studies showed that vitamin D3 was statistically superior in raising both levels.
Toxicity Level of Vitamin D
A daily intake of 20,000 IU over an extended period of time (as in multiple months) can produce toxic effects in adults. Long term dosages of more than 1,800 IU daily may cause hyper-vitaminosis D in children. Signs of excess are unusual thirst, sore eyes, itching skin, vomiting, diarrhea, urinary urgency, abnormal calcium deposits in blood vessel walls, liver, lungs, kidney, and stomach.
For these reasons, it is important to consult your physician after a test evaluation to find out what would be the optimum vitamin D3 daily dosage for you. A very safe and conservative range of vitamin D3 daily intake would be around 400 to 1,000 International Units (IU).
Other Vitamin D Considerations
Vitamin D synthesis in the skin declines with age. If you are over sixty you may consider taking additional 1,000 IU daily over the normal maintenance amount.
Anyone with Crohn’s disease, cystic fibrosis, or celiac disease is at risk of being deficient in vitamin D and should have their blood levels checked.
Low levels of vitamin D can cause a dip in a hormone that regulates appetite, impairing the brain’s signal that you are full, leading to unwanted weight gain.
Night workers, people who live in areas of long winter periods and others whose lifestyle keeps them from sunlight, should increase vitamin D in their diet and supplementation.
Dark-skinned people living in the northern climates also might want to increase their vitamin D intake.
Pregnant women who have low levels of vitamin D are more likely to give birth by cesarean section.
Do not supplement vitamin D for your dog nor cat unless your vet specifically advises it.
Antacids used for acid reflux may decrease levels and availability of vitamin D.
Because vitamin D supplement is fat soluble, it is recommended that you take it with food.
Vitamin D is responsible for maintaining normal blood levels of calcium and phosphorus, and helping to build strong bones.
Vitamin D works with other vitamins, minerals and hormones to promote bone mineralization.
Studies also show that Vitamin D may improve mood.
You are welcome to consider the vitamin D3 that we recommend by clicking this link.
Resources and Acknowledgment:
(1) New Vitamin Bible by Dr. Earl Mindell, Revised Edition 2011
(2) Vitamin D vs. D3: Differences, similarities, and which is better for you, By KRISTI C. TORRES, PHARM.D. | FEBRUARY 25, 2020
(3) https://pubmed.ncbi.nlm.nih.gov/18492750/
(4) https://academic.oup.com/jcem/article/101/8/3070/2835033