Vitamin D is very popular on the supplemental market, but it comes in many different forms, so how do you identify it?


1. Active Form of Vitamin D : commonly found in medicines.

2. Inactive Form of Vitamin D : mainly used in dietary supplements. Inactive vitamin D generally can be divided into D3 and D2.

The difference between "active" vitamin D and "inactive" vitamin D is that "inactive" vitamin D needs to be metabolized by the body before it becomes "active" for the human body to use, so it represents an additional layer of the body's control and regulation mechanism. Active D3 acts directly after ingestion. Although the effect is fast, it means that there is relatively less body control mechanism. Therefore, it is necessary to be very careful when taking it to avoid excessive side effects. Therefore, active form of vitamin D must be taken under the advice and supervision of medical personnel, and always pay attention to possible side effects such as nausea and vomiting. If you experience unwell symptoms, stop taking immediately and seek medical help.

There is another way to identify the form of vitamin D, the English term of "active" vitamin D3 is “Calcitriol” whereas "inactive" vitamin D3 is “Cholecalciferol”. "Active" vitamin D3 is usually labeled with micrograms (common doses are 0.25 micrograms per capsule), while "inactive" vitamin D3 may range from 100-800 IU. Internet rumors have it that as long as it is labeled with micrograms, the D3 is the active form; on the other hand, when it is labeled with IU, the D3 is supposed to be the inactive kind. In fact, this saying is not completely correct. According to the regulations announced by the Ministry of Health and Welfare, food-grade inactive vitamin D needs to be marked with both international units (IU) and weight units (micrograms), and these two can be fixedly converted. The international conversion method for vitamin D is 1 microgram (ug) = 40 IU; therefore, 5 micrograms of inactive vitamin D3 equals 200 IU of vitamin D, and these two units need to be both labeled on the packaging.


In the "Dietary Reference Intakes (DRIs)", vitamin D is recommended to be 10 micrograms (400 IU) per day for infants and young children, and at least 10 micrograms (400 IU) per day for adults. For people age over 51, 15 micrograms (600 IU) per day is recommended. As for the daily "Tolerable Upper Intake Levels (UL)" part, the daily upper limit for infants and young children aged 0-12 months is 25 micrograms (1000 IU), and from aged 1 to adults, the daily upper limit is 50 micrograms (2000 IU).

As for the standard in the United States, it is even higher. According to the National Institutes of Health (NIH), The Tolerable Upper Intake Level for infants 0-6 months is 1000 IU per day; The Tolerable Upper Intake Level for infants 7-12 months is 1500 IU per day. Besides, children 1-3 years : 2500 IU per day ; children 4-8 years : 3,000 IU per day ; children aged 9 years and older, adults, pregnant and breastfeeding women : 4000 IU per day.


Serum vitamin D testing is currently available in many medical institutions to measure the level of vitamin D [ 25(OH)D ] in the body. According to the general recommended value, the level of vitamin D in the body :

<20 ng/mL:Vitamin D Deficiency. The US NIH is set at 12 ng/mL

<30 ng/mL:Vitamin D Insufficiency

≥30 ng/mL:Normal

≥60 ng/mL:There may be potential side effects

Therefore, if you want to know the vitamin D levels in your body, you can go to a medical center to do a 25(OH)D test.


The benefits of vitamin D are many, including enhancing calcium absorption, helping the growth and development of bones and teeth, promoting the release of bone calcium to maintain blood calcium levels normal, and helping to maintain the normal physiology of nerves and muscles. In fact, there are many more health benefits of vitamin D have be proven abroad. In the clinical survey of Taiwanese people, there are actually quite a lot of people have vitamin D Insufficiency. Therefore, normal daily supplementation is needed to maintain healthy and regulate physiological functions.

Food-grade inactive vitamin D can be divided into vitamin D2 and vitamin D3. A study published in the Journal of Clinical Endocrinology & Metabolism in 2011 (Robert P. Heaney, 2011) pointed out that vitamin D3 was found to be 87% more effective than vitamin D2 in increasing the level of vitamin D in the body. Another 2015 study (Beatriz Oliveri, 2015) found among testing subjects, those taking vitamin D3, even after stopping supplementation, maintained higher levels for up to 77 days than those taking vitamin D2. Hence, international experts and professional organizations mostly recommend direct supplementation of vitamin D3, which is considered more effective than vitamin D2.


For healthy adults, we would recommend maintaining 25(OH)D levels between 30-50 ng/mL. In general food, such as fish, eggs, milk, etc., all contain vitamin D, which can be supplemented normally on a daily basis. However, it is hard to supplement the body's vitamin D needs through diet alone. Sun exposure can also promote the synthesis of vitamin D, but it will also be affected by weather, latitude, sun exposure time, etc., so it is not good enough. In addition, sun exposure might cause some damage, such as darkened skin, sunburned or spots; furthermore, ultraviolet rays could be harmful to the eyes. Therefore, it is generally recommended that dietary supplements are a more effective way in terms of vitamin D supplementation.

To conclude, for vitamin D supplementation, inactive form of vitamin D3 is the top choice; 400-800 IU is advised for basic health care daily. If you want to supplement a higher level, there are many large-scale research or professional institutions abroad have pointed out that taking 2000 IU or 4000 IU per day is safe. However, if you supplement with a higher dose of vitamin D, unless it is a special group, or a special purpose, short-term supplement or under the advice of a medical professional, it is still recommended that high-dose supplements should be followed by regular blood tests.

Although daily vitamin D3 supplementation is recommended, nutritional supplements are only supplements. Maintaining a healthy and balanced diet, keeping proper outdoor exercise and sun exposure are still important tips for staying health.