Vitamin D has been in the news a lot lately. In actuality, Vitamin D is in the news all the time, as research is finding that a large portion of the population needs to supplement vitamin D in order to achieve ideal levels. However, every person has unique needs for vitamin D; in this post, we’ll show you how you can determine the exact amount of vitamin D that you need.

Today’s post comes to us from our friends at Natural Path Health Center.

Research supporting vitamin D supplementation has increased dramatically over the the past two decades. In the past, vitamin D was mainly thought of as a nutrient important for bone health. However, recent research has shown that low vitamin D levels can lead to or exacerbate a number of acute and chronic conditions, including muscle pain and weakness, autoimmune diseases (such as type 1 diabetes), colorectal cancer, cardiovascular disease, inflammatory bowel disease, multiple sclerosis and immune dysfunction. These findings have prompted controversy in defining “optimal” serum levels of vitamin D, as well as the doses needed to achieve them. In this post, I’ll review key conclusions of recent studies on vitamin D and address the question of optimal dosing of vitamin D for the prevention of chronic disease.

Ideal Values of Vitamin D – Why are the values I read about so different?

The Institute of Medicine (IOM) sets the dietary reference intakes (DRIs) for vitamins, with the intention of serving as a guide for good nutrition and to provide the basis for nutrient guidelines in the U.S. and Canada. In the case of vitamin D, determining the DRI is a complex process. Unlike other vitamins, serum levels of vitamin D are the result of dietary intake, supplementation and synthesis within the skin after exposure to UVB sunlight. All of these factors vary from person to person (and time of year), making the determination of “optimal” vitamin D intake difficult for the general population.

In determining vitamin D intake guidelines, the IOM only considered studies on vitamin D and bone health, largely ignoring research on vitamin D and other chronic health conditions, which often indicate the need for higher serum vitamin D levels. This, along with the fact that large segments of the population already suffer from inadequate vitamin D status and that very few cases of vitamin D toxicity have ever been reported/documented call into question the values recommended by the IOM. Lastly, if one looks closely at the IOM recommendations, they stress that the current cut-off points of sufficiency and deficiency for 25-hydroxy vitamin D (25(OH) D) used by laboratories have not been set using rigorous scientific studies. This is another reason why the values deemed sufficient by major laboratories and/or government agencies may differ from those recommended by the latest research.

The IOM reference data, which assumes that sun exposure contributes a meaningful amount of vitamin D to those in North America (which appears to be incorrect – more on that in a moment) has set a target serum level of 20 ng/ml (50 nmol/L – to convert from ng/ml to nmol/L, just multiply by 2.5). However, recent studies have shown this level to be insufficient for the prevention of chronic vitamin D-associated disorders. In fact, recent research has shown that values less than 30-32 ng/ml (75-80 nmol/L) should be classified as “low” and that a therapeutic target of 40-70 ng/ml (100-175 nmol/L) may be necessary for people with vitamin-D mediated chronic disease conditions. In fact, the Vitamin D Council recommends a target level of 50-80 ng/ml, year-round.

How to Optimize Your Vitamin D Dose

As stated earlier, a person’s vitamin D status depends on dietary intake (mainly through fatty fish, eggs and beef), supplementation and synthesis due to UVB sunlight exposure. Unless a person eats fatty fish (like trout or salmon) every day, they are likely to get very little vitamin D from foods. Likewise, vitamin D production as a result of exposure to the sun is quite variable and is significantly reduced as a result of sunscreen use and more time spent indoors. In addition, research has now shown that except for the summer months, the skin makes little if any vitamin D from the sun at latitudes above 37 degrees north (shown as the shaded region on the map).

People that live in these areas are at a greater risk for vitamin D deficiency. Therefore, vitamin D supplementation may be the only way for the majority of the US population to optimize their vitamin D levels.

Research has indicated that 1 mcg or 40 IU per day increases 25(OH) D by an average of 0.4 ng/mL (1 nmol/L) when given over a 3-4 month period for a healthy adult (weighing approximately 150 lbs.).Therefore, a normal weight healthy adult with an initial level of 15 ng/ml would require about 4000 IU per day to achieve a level of 55 ng/ml when given over 3-4 months.

A caveat to this is that body weight, and more specifically body fat, can dramatically increase a person’s vitamin D needs. In fact, in the absence of significant UVB exposure, research indicates that supplemental vitamin D needs of approximately 1000 IU (25 mcg) per day for every 15 kg of body weight may be needed. Therefore an obese 150 kg (330 lbs.) adult may require 10,000 IU per day or more to achieve a 25(OH) D level of 50 ng/ml when taken over 3-4 months. In cases of more severe vitamin D deficiency (serum levels of >15 ng/ml or 37 nmol/L), some studies have suggested loading doses of 50,000 IU once weekly for 2-3 months or 3 times weekly for one month, in addition to 800-2000 IU per day (regardless of the loading dose pattern chosen) may be necessary to prevent recurrent deficiency.

Once optimal serum vitamin D levels have been achieved, research indicates that a daily dose of 4600 IU (115 mcg/day) of supplemental vitamin D3 was found to be necessary for most people to maintain serum 25(OH) D levels between 30-88 ng/ml (75-220 nmol/L).

Should I Take Vitamin D2 or D3?

The short answer – use vitamin D3.

To elaborate, the use of vitamin D2 started in the 1930s based on the availability of prescription vitamin D2 for the prevention of rickets. This led to the long-term assumption that vitamin D2 and D3 were equally effective in humans. However, there is a lack of consistent and objective evidence that the two forms of vitamin D are equivalent in regards to increasing serum 25(OH) D levels. In fact, a growing number of studies over the past decade have found that D3 increases serum 25(OH) D levels much more efficiently than D2 (70-87% greater = 1.7-1.9 times greater). This is likely because the serum half life of D3 is longer.


Based on the available evidence, the majority of people in North America could substantially reduce their risk of vitamin D-associated disorders – including osteoporosis, muscle pain and weakness, autoimmune diseases (such as type 1 diabetes), colorectal cancer, cardiovascular disease, inflammatory bowel disease, multiple sclerosis and immune dysfunction – by taking supplemental vitamin D3. Each person should get a baseline test completed (testing for 25-hydroxy vitamin D (NOT 1,25 OH vitamin D)) to get an idea of how much vitamin D they will need to reach the optimal range of 50-80 ng/ml.

Each person will need between 40 IU (1 mcg) of vitamin D3 to increase their serum 25(OH) D levels by 0.4 ng/ml (1 nmol/L)  and 1000 IU (25 mcg) per day for every 15 kg of body weight when taken over a 3-4 month period. Those with severe vitamin D deficiency (less than 15 ng/ml (37 nmol/L) may need to start with a loading dose of 50,000 IU 3 times weekly for one month in addition to 800-2000 IU per day for 3-4 months to reach this level.

After 3-4 months, obtain another 25(OH) D test and adjust your dosing accordingly. Once a person has achieved their ideal serum 25(OH) D level, they should continue on approximately 4600 IU per day to maintain that level (use testing to guide you).

As a final note, there is some research that vitamin D and vitamin K work in synergy with one another to support bone health and that taking high doses of vitamin D may increase the demand for vitamin K. However, conclusive evidence to support this finding is lacking. However, the synergistic relationship between vitamin D and vitamin K warrants monitoring serum K levels  (or uncarboxylated osteocalcin levels) and supplementing vitamin K as necessary – generally 80-180 mcg of Vitamin K2 (MK-7), along with vitamin D3.

Recommended daily dosages of vitamin D3 (IU) – Vitamin D Council

  • 1 & younger: 1000 IU
  • 1 & older: 1000 IU per 25 lbs.
  • Adults: 5000 IU
  • Blood testing: every 2-3 months


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