If you are unsure about the correct dosage for your vitamin D supplement, then you're not alone!
Although medical doctors and scientists agree that supplementation is the best way to prevent a vitamin D deficiency, there is a considerable discrepancy among the recommended vitamin D dosages by different experts and medical organizations.
For example, 100 IU of vitamin D per day was officially considered adequate to prevent skeletal deformities in the 1940s.
Later, the recommended vitamin D intake was increased to 200 IU daily, which was considered sufficient for both children and adults.
But after the 1970s, doctors finally developed clinical tests for measuring vitamin D levels. Once their widespread use began, they estimated that more than one billion people worldwide were either vitamin D deficient or insufficient (1).
In reality, the most optimal intake will vary from person to person. It depends on individual factors such as your basal vitamin D levels, body weight, lifestyle, use of sunscreen, etc.
Keep reading to discover the most suitable dosage recommendations for you and how much is too much to ensure you get sufficient vitamin D.
What is the recommended vitamin D dosage?
How to get your daily dose of Vitamin D
Did you know that there is more than one way to obtain vitamin D? That’s because it is a fat-soluble vitamin that can successfully accumulate in your body.
Therefore, taking a larger dose of the sunshine vitamin will lead to a prolonged elevation of the vitamin D levels in your blood.
Instead of daily supplementation, you can take a single larger dose once a week or even once a month, which will have a prolonged effect.
For example, one study reported that taking a single loading dose of 150 000 IU led to the continuous elevation of vitamin D levels after 14 and 28 days (2).
The increase after 28 days was higher than daily supplementation with a 30x lower dose. However, the daily dosing led to a faster and more predictable increase in serum vitamin D levels.
Therefore taking a dietary supplement once per day is a more reliable method.
How will the dosage affect your blood levels of vitamin D?
According to the majority of guidelines, adults should supplement with at least 600 IU (15 mcg) of vitamin D to achieve a minimum of 20 ng/ml (50 nmol/l) 25-hydroxy vitamin D (3, 4, 5).
25-hydroxy vitamin D is a biomarker for vitamin D level status, and values below 20 ng/ml indicate a deficiency.
However, the Endocrine Society recommends achieving 25-hydroxy vitamin D levels of at least 30 ng/ml (75 nmol/l) as they appear optimal for your health (6). Patients with vitamin D levels under 30 ng/ml (75 nmol/l) are considered insufficient.
Since the optimal vitamin D dosage depends on your current vitamin D status and most people are insufficient or deficient, the Endocrine Society recommends supplementing with higher doses.
If you are insufficient, it's estimated that you may need at least 1,500–2,000 IU (37.5 to 50 mcg)/day to maintain levels above 30 ng/ml.
If you are deficient (your 25-hydroxy vitamin D levels are under 20 ng/ml), you are at high risk of bone-related conditions such as osteoporosis (7).
Thus, you may need to supplement with at least 3 000 IU (75 mcg) per day for several months to achieve optimal vitamin D levels.
Patients with 25-hydroxy vitamin D levels under 12 ng/ml (30 nmol/l) have a severe deficiency and are at an immediate health risk and increased susceptibility to infections. Scientists also argue that such critically low vitamin D levels increase overall mortality.
If your levels are under 12 ng/ml, you may need supplementation with a high dose of at least 4 000 IU (100 mcg) per day, and it will still take a few months to achieve optimal vitamin D levels.
Other factors affecting vitamin D dosage
Another factor affecting vitamin D dosage is your body weight or fat mass. You may need a higher vitamin D dose to achieve a specific blood level if you have a higher body fat percentage.
That’s because vitamin D is a fat-soluble vitamin that accumulates quickly in the fat tissue. Higher amounts of adipose tissue remove more vitamin D from the blood and lower your levels.
Scientists have reported an adverse association between body mass index and response to vitamin D supplementation (8).
One study investigated the effects of supplementation in 17,614 healthy older adults (9).
The data revealed that overweight people need about 50% higher doses, and obese people need up to 2.5x the usual amount to reach the same 25-hydroxy vitamin D levels as individuals with average body weight.
This means that an obese person may need to supplement with 4 000 IU to maintain 25-hydroxy vitamin D above 30 ng/ml simply.
Other factors that may affect the dosage of vitamin D supplementation may include the season, any medications, regular use of sunscreen, etc.
What are the symptoms of vitamin D deficiency?
Vitamin D deficiency can lead to serious bone health problems in both children and adults. In children, the condition is also known as rickets, while adults may develop osteomalacia.
The name “osteo-malacia” means “soft bones.” The lack of vitamin D leads to low levels of bioavailable calcium and problems with bone mineralization which results in weak bones (10).
Osteomalacia can lead to debilitating pain, bone deformities, dental abnormalities, tetanic spasms, and seizures due to the low serum calcium (11).
In addition, the sunshine vitamin is essential for muscle strength. A low vitamin D level in your blood can lead to muscle weakness and an increased risk of falling. In combination with bone health problems, this raises the risk of bone fractures.
Furthermore, vitamin D deficiency and insufficiency may negatively affect the immune system, increasing the risk of infections and illness (12).
Vitamin D supplementation is currently being studied for combating other conditions, including depression, cardiovascular disease, autoimmune disorders, etc.
Can you get vitamin D without supplementation?
Besides supplementation, your body can produce or absorb vitamin D from food sources.
The endogenous synthesis of vitamin D is the primary evolutionary mechanism of preventing a deficiency in the human body. The process occurs in the skin under the effect of direct sunlight (13).
However, sun exposure is often insufficient in most modern people due to several factors:
- we are spending too much time indoors
- a sedentary lifestyle is more common than ever
- most people use sunscreen as a skin cancer prevention
- anthropogenic air pollution blocks the UVB rays required for the endogenous synthesis of vitamin D
On the other hand, there are only a few good dietary sources of vitamin D. They include fatty fish, egg yolks, mushrooms, and fortified foods.
Fatty fish is considered the best dietary source of vitamin D. Yet, only some subspecies, such as wild salmon (and to a much lesser extent farmed salmon), contain sufficient amounts of vitamin D (14).
Egg yolks can also be a good source of vitamin D as long as they are from free-range and pasture-raised chicken which had adequate sun exposure (15).
Mushrooms are considered the best non-animal source of vitamin D. Keep in mind that vitamin D is high only in wild mushrooms or those grown under UV light (16).
In addition, there are several fortified food options, such as fat spreads, cereals, milk, and dairy products.
How much vitamin D is too much?
Vitamin D is a fat-soluble vitamin, and as such, it can accumulate in the body. Too much of it can lead to toxic effects or even death in extreme cases. This may occur when serum 25-hydroxy vitamin D reaches 150 ng/ml (375 nmol/l).
That said, it’s not likely to overdose with vitamin D from food or sun exposure.
The majority of the cases of toxicity are due to taking supplements such as vitamin D tablets. Other causes, such as congenital diseases and lymphomas, are much rarer (17).
Scientists suggest that doses up to 10 000 IU per day may be safe for prolonged supplementation since they will lead to 25-hydroxy vitamin D levels under 140 ng/ml in most cases (18).
Toxicity may occur in continuous supplementation with doses above 10 000 IU per day for longer than three months or more than 300 000 IU in 24 hours (19).
Excess vitamin D leads to elevated calcium levels in the blood; a condition called hypercalcemia. Symptoms of vitamin D toxicity may include:
- loss of appetite
- irregular heart rhythm
- formation of kidney stones
In most severe cases, elevated serum calcium levels can lead to arrhythmia and kidney failure, which are potentially fatal.
A high calcium level in your blood may also increase the long-term risk for soft tissue calcification, including calcification of your blood vessels and atherosclerotic complications.
Can I take vitamin D with my medications?
Remember that several medications may lower your vitamin D levels by reducing absorption. They include:
- cholesterol-lowering drugs
- weight loss drugs
- stimulant laxatives
In addition, anticonvulsants may increase the breakdown of vitamin D and thus reduce the effectiveness of supplementation (20). Therefore, you may have to increase your vitamin D dosage to achieve optimal serum levels.
On the other hand, some drugs may require you to reduce the dosage of your vitamin D supplement due to an increased risk of adverse reactions.
Several medications may increase the risk of hypercalcemia, and taking high doses of vitamin D with them should be avoided. Examples include:
- Remedies for psoriasis
- Heart medications
- Thiazide diuretics
Taking vitamin D supplements during therapy with statins (cholesterol-lowering drugs) may also affect the way your body processes the medication and increase its side effects.
What is the best form of vitamin D
Vitamin D is actually a combination of several compounds, with the most important ones being D2 and D3. They are the forms of vitamin D found in the human body and in different foods and dietary supplements.
D2 can be found in plant products (mushrooms), while D3 (cholecalciferol) can be found in the human body and animal products (fish, yolks). In addition, D3 can be produced by some algae.
According to research, vitamin D3 leads to a higher increase in serum D levels (21). It also likely has a longer shelf life as a supplement compared to D2 (22). Therefore, it’s generally considered best to supplement with D3 instead of D2.
In addition, you should consider taking a supplement that contains a combination of vitamin D3, vitamin K2, and calcium. These vitamins have synergistic effects and help direct the calcium to your bones and away from blood vessels.
The vitamin D3 and vitamin K2 combo leads to a higher bone mineral density and more benefits for bone health than vitamin D alone. At the same time, the synergistic effects prevent the calcium from depositing in your arteries (23).
Furthermore, combining vitamin D with small amounts of calcium also provides further benefits in several studies (24, 25, 26).
To ensure optimal absorption of your supplement, you should always take it with a meal rich in fats, preferably your biggest meal of the day (usually lunch or dinner).
Additionally, taking a supplement with Bioperine (black pepper extract), such as Vitamin D3 + K2 Complex by Nutririse, may further boost its absorption.
Bioperine is known to slow down intestinal passage and block the process of glucuronidation in the liver (27, 28). This increases the absorption and bioavailability of your supplement.
Note: This article is for informational purposes only, and not intended for use as medical advice. Always consult your healthcare provider before starting any dietary supplement.