Adjusting Your Vitamin D Intake to Optimal Levels

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With the increasing worldwide news coverage of widespread vitamin D deficiency and the high rates of associated diseases such as type 2 diabetes, cardiovascular disease, depression, and autism, you may wonder just how much vitamin D is too much? Many doctors are clueless about vitamin D toxicity and believe that 2000 IU per day of vitamin D3 on a daily basis could be deadly, and 100,000 IU in one dose would surely kill you. Surprising to some, these common beliefs of doctors are grossly mistaken. New research argues for 10,000 IU per day of vitamin D3 on a daily basis for long periods being the upper recommended limit for adult dietary intake and that single doses of 100,000 IU are helpful for rapidly building up levels of vitamin D in the body.

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Upper Limit for Vitamin D3 Intake

It is commonly believed by doctors today that 2000 IU per day of vitamin D3 is the upper safe limit for adult dietary intake. However, like many “medical facts” this appears to be an errant belief. An analysis of research on vitamin D toxicity has found that there is little to no documented evidence of toxicity for vitamin D3 intake of 10,000 IU per day or less. Even at 50,000 IU per day for 8 weeks in at least one study, there was no evidence of vitamin D toxicity.

(from Risk assessment for vitamin D)

The objective of this review was to apply the risk assessment methodology used by the Food and Nutrition Board (FNB) to derive a revised safe Tolerable Upper Intake Level (UL) for vitamin D. New data continue to emerge regarding the health benefits of vitamin D beyond its role in bone. The intakes associated with those benefits suggest a need for levels of supplementation, food fortification, or both that are higher than current levels. A prevailing concern exists, however, regarding the potential for toxicity related to excessive vitamin D intakes. The UL established by the FNB for vitamin D (50 µg, or 2000 IU) is not based on current evidence and is viewed by many as being too restrictive, thus curtailing research, commercial development, and optimization of nutritional policy. Human clinical trial data published subsequent to the establishment of the FNB vitamin D UL published in 1997 support a significantly higher UL. We present a risk assessment based on relevant, well-designed human clinical trials of vitamin D. Collectively, the absence of toxicity in trials conducted in healthy adults that used vitamin D dose 250 µg/d (10 000 IU vitamin D3) supports the confident selection of this value as the UL.

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Optimal Target Range for Vitamin D

Based upon review of many references of vitamin D research done in the last few years, it appears that there is a nearly universal agreement that blood serum levels of 25(OH)D, the most common form of vitamin D in the body, should be at least 32 ng/mL (equivalent to 80 nmol/L) to significantly reduce the risk of vitamin D deficiency related diseases.

However, an optimal level on this blood test appears to be somewhere between 50 ng/mL to 80 ng/mL (equivalent to 125 nmol/L to 200 nmol/L). There is little evidence of adverse health effects from vitamin D levels until the 25(OH)D test yields measurements well above 100 ng/mL (250 nmol/L). Even if you overshoot with your vitamin D supplementation by a factor of two, it is not likely you will create bad health effects so long as you don’t exceed that level for more than a few months before catching it via a blood test.

Sun Exposure Is Major Influence on Vitamin D Levels

The blood serum level of vitamin D depends a lot upon factors such as how much bright sunlight you get each day and the color of your skin. As you may know, ultraviolet B light striking human skin causes the skin to generate vitamin D.

Very dark skin may take 5 times or more the sun exposure as a light-skinned Caucasian to generate the same amount of vitamin D in the skin. This is likely to be a very significant and common issue affecting vitamin D levels for people with strong ancestry from places such as Africa, Tamil Nadu, and Sri Lanka in which the natives adapted to the intense sunlight by increased levels of melanin in the skin.

Asians and mixed-race people with moderate levels of melanin in their skin are also at higher risk for insufficient vitamin D levels compared to individuals with little melanin in their skin such as most Caucasians.

If you’re a Caucasian working outdoors around mid-day for half an hour each day without sunblock or other sun protection, your skin is likely generating more than 20,000 IU of vitamin D3 per day. The skin limits the generation of vitamin D as excessive sun exposure increasingly causes destruction of vitamin D. This will likely start to limit vitamin D accumulation from sun exposure before sunburn begins.

(from Risk assessment for vitamin D)

Sun exposure
The maximum amount of vitamin D that is cutaneously produced under UV light stimulation, creating serum 25(OH)D concentrations similar to those resulting from an oral dose of 250 µg, occurs principally at full-body erythemic light exposures (95) and consequently is unlikely to occur frequently. Low and moderate levels of UV light exposure stimulate vitamin D production, but prolonged exposure destroys vitamin D in the skin (96). There are no known cases of vitamin D toxicity resulting from extreme or unusually prolonged sun exposure. Chronic exposure to sunlight in outdoor workers at the end of the summer season produce serum 25(OH)D concentrations equivalent to those with an oral intake of 70–125 µg vitamin D/d (43). Given seasonal and latitudinal variations in sun exposure, the amount of time spent indoors by most of the population, and the off-setting effects in skin synthesis, long-term vitamin D production from sun exposure is unlikely to exceed 125 µg/d in North America and Europe.

Food Intake of Vitamin D is Highly Variable

Most foods eaten by the typical person don’t have much vitamin D in them. The exceptions are fish such as salmon and tuna, organ meats such as liver and kidney, and medicinal foods such as cod liver oil. Most people do not eat these often. As a result, you should probably not count on your regular food intake to contribute a significant amount of vitamin D.

(from Vitamin D and Mental Illness)

Although vitamin D is technically a vitamin, according to Stedman’s Medical Dictionary definition of the word, significant amounts of vitamin D are not found in the foods humans naturally consume. A hundred years ago, after we were steadily migrating out of the sun and into buildings, cars, and layers of sun block, Northern Europeans realized that adding a teaspoon of fish oil to infants’ diets helped them thrive. How did we decide how much to add? We guessed based on animal models of rickets. Correctly, it turned out, to prevent rickets in children, but since the same dose was applied to adults, the adult dose was off by a factor of ten. This mistake continues to this day.

You may rightly point out that vitamin D is added to milk and dairy products and that these foods therefore have significant levels of vitamin D compared to the unfortified versions. However, that’s often only true of liquid milk, margarine, and similar products. Ice cream, yogurt, and cheeses are usually made with milk that is not fortified with vitamin D.

Furthermore, many of the people who are most at risk for vitamin D deficiency are the least likely to consume vitamin D fortified products due to lactose intolerance:

(from The Bioavailability of Vitamin D from Fortified Cheeses and Supplements Is Equivalent in Adults)

Thus, populations in North America often rely on fortified foods and dietary supplements to meet their vitamin D needs during times of insufficient sunlight. Vitamin D fortification is mandatory in Canada for beverage milk (100 IU/250 mL)9 and margarine (53 IU/10 g) (35) and optional in the United States for milk, breakfast cereals, and calcium-fortified fruit juices (40–140 IU/serving) (36). However, cross-sectional studies suggest that current North American fortification practices are not effective in preventing vitamin D insufficiency, because fortified foods provide inadequate amounts of vitamin D and are often underfortified (1,27,37–39). Furthermore, milk consumption has declined considerably since the 1980s (40) and lactose intolerance is a common problem, particularly among populations that are at greatest risk of vitamin D deficiency (e.g. Blacks, Asians, Native Americans) (41,42). Clearly, additional foods need to be fortified with vitamin D to increase the availability of this essential nutrient for the general population.

Even if you eat and drink the same foods containing vitamin D supplementation in the same quantities every day, there is a strong chance the levels of vitamin D in that food will be inconsistent. Testing of products such as milk that are routinely supplemented with vitamin D show that they often have much less vitamin D content than stated on the label.

It’s my opinion based upon reading many studies on vitamin D in nutrition and medicine that most people should consider their food intake as an iffy and relatively unimportant source of vitamin D because:

  1. Most foods don’t have much vitamin D in them.
  2. There is a high variability in vitamin D content in even fortified foods that should have a more consistent level of vitamin D.
  3. Consuming vitamin D fortified foods will not allow most people to attain adequate levels of vitamin D unless they eat unrealistically large quantities of them that would likely result in excessive calorie intake.
  4. Vitamin D intake in food varies widely from day to day for most people who eat a varied diet.
  5. Many people who are at the highest risk for vitamin D insufficiency due to dark skin also suffer from lactose intolerance which means their intake of common vitamin D fortified dairy products is likely to be lower.

Therefore, in the discussion below about adjusting your vitamin D levels to optimum, I intentionally skip over the amount of vitamin D in food. The typical food quantities of vitamin D are “noise” in the data when compared to the amount obtained from sun exposure and high-dosage vitamin D supplements.

If you are quite certain about the vitamin D content in your food and eat very high vitamin D foods with great consistency and frequency, you may be an exceptional case and my thoughts above regarding ignoring vitamin D in your food may not pertain to you. In that case, it may be reasonable for you to account for the vitamin D in your food when considering how to achieve optimal vitamin D levels.

Guideline Dosages for Adults

Vitamin D3 dosages are generally expressed in IU (International Units), but many medical studies use micrograms (µg) to denote the dosage or dietary intake. For reference, 250µg is equivalent to 10,000 IU. In recent research, 10,000 IU per day is suggested as a realistic upper limit for total vitamin D dietary intake.

For people 18 and over who get infrequent exposure to bright sun, you can get a ballpark estimate of vitamin D blood levels by taking the total amount of vitamin D in the diet (including supplements) measured in IU and dividing by 100 to get an approximate blood level measured in ng/mL. This is just a ballpark, it would not be surprising if it is off by a factor of two. So to be sure, you really have to get a 25(OH)D vitamin D blood test.

Given this ballpark number and minimum and optimal ranges, for an adult who gets little exposure to the mid-day sun on most days it would be reasonable to estimate that taking 3200 IU of vitamin D3 per day would be about the right amount to achieve 32 ng/mL levels which are considered on the low end of the desirable range. To attain an optimal level of 65 ng/mL, midway in the optimal ranges from 50 ng/mL to 80 ng/mL suggested by several studies, you would likely need about 6500 IU of vitamin D3 per day. For people without daily mid-day sun exposure, this is probably nearly impossible to achieve without consuming vitamin D3 supplements.

Determining Your Vitamin D Levels

Vitamin D levels are best measured by the 25(OH)D test which costs about $45 to $65 per test. You may have to pay for this test from your own pocket as the government and many insurance plans are playing Russian Roulette with your long-term health to “save money”.

If you have a flexible healthcare spending plan or section 125 plan via your workplace, considering setting aside enough money to get these tests once or twice per year for each family member. This will allow you to use pre-tax dollars to pay for the tests.

Vitamin D tests for about $45 to $65 are available via Life Extension Vitamin D, 25-Hydroxy Blood Test, Vitamin D test, or via these links:

Order Today

Life Extension Blood Testing

If you’re willing to spend some time filling out a six page long health survey (click here for a sample) and retest and update your health information every 6 months, then you can get a home vitamin D testing kit for $40.00 twice per year. Visit the GrassrootsHealth web page D*Action Participant Questionnaire for more information or to fill out a survey and purchase your test kit. GrassrootsHealth is affiliated with University of California at San Diego and many doctors in San Diego County, California.

Accounting for Vitamin D2 Lower Effectiveness

If you use any supplements that contain vitamin D2 (ergocalciferol) rather than vitamin D3 (cholecalciferol), you have to account for the difference in effect. Take those dosages of vitamin D2 and divide them by 1.7 to get an approximate equivalent of vitamin D3. For example, 400 IU of vitamin D2 is like 235 IU of vitamin D3.

(from Vitamin D and Mental Illness)

For those who want to avoid the sun or artificial light sources, cholecalciferol is the preferred form of vitamin D. It is the compound your skin makes naturally when exposed to UVB. It is more potent and is safer than the synthetic analog, ergocalciferol, in more common use. Vieth R, Chan PC, MacFarlane GDEfficacy and safety of vitamin D3 intake exceeding the lowest observed adverse effect level.Am J Clin Nutr 2001 Feb;73(2):288–94. Cholecalciferol is 1.7 times more efficient at raising 25(OH)D levels than is ergocalciferol. Trang HM, Cole DE, Rubin LA, Pierratos A, Siu S, Vieth REvidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2.Am J Clin Nutr. 1998 Oct;68(4):854–8. If oral cholecalciferol is the only source of vitamin D (complete lack of UVB exposure), between 3,000–5,000 IU per day will be needed to ensure serum 25(OH)D levels in the desirable range. Vieth R, Chan PC, MacFarlane GDEfficacy and safety of vitamin D3 intake exceeding the lowest observed adverse effect level.Am J Clin Nutr 2001 Feb;73(2):288–94.

Action Plan for Optimizing Your Vitamin D3 Levels

Here’s a simple plan to discuss with your doctor or healthcare expert to fine-tune your vitamin D levels in a matter of several months. This is best suited for adults without much vitamin D generated from sun exposure. It also assumes you get the vast majority of your vitamin D from supplements as that means you can easily estimate your daily vitamin D dosage by adding up the amounts of vitamin D3 in all your supplements.

  1. Take 10,000 IU of vitamin D3 per day for 7 days. Consume the supplements with the meals you eat that have the highest fat content as vitamin D dissolves well in fat. This will quickly bump up any really low levels of vitamin D, but is less likely to cause overshooting of target ranges than multiple doses of 100,000 IU as some studies have used.
  2. Take a consistent daily dosage of around 5000 IU of vitamin D3 for 60 days. If you are using supplements that are 2000 IU each, then take 4000 IU or 6000 IU per day for 60 days.
  3. Get a 25(OH)D blood test to measure your blood level of vitamin D.
  4. Pick a target level for your 25(OH)D measurement of vitamin D in your blood serum measured in ng/mL. 65 ng/mL is a reasonable target based upon current research, but you should discuss this with your doctor or healthcare expert whom you trust has been brought up to date on recent vitamin D findings.
  5. Take the result from your blood test and use it to determine how vitamin D3 affects your blood serum vitamin D levels. Do this by estimating how your daily 5000 IU of vitamin D3 corresponds to the measured level in your blood. For instance, if your blood test shows that you have 55 ng/mL and you get about 5000 IU from dietary supplements, then compute 5000 / 55 to get 90.9. This means that it takes about 90.9 IU of vitamin D3 per day to get 1 ng/mL of measured 25(OH)D in your blood.
  6. Take your target blood serum 25(OH)D level determined earlier in ng/mL and multiply it by the number you computed above in the previous step. For instance, if we picked a target of 65 ng/mL and use the 90.9 number from the previous computation, then we multiply 65 by 90.9 to get 5908.5 IU of vitamin D3 per day.
  7. Take the computed dosage from the previous step and determine how to spread it across the dietary supplements you take each day. For instance, you could get close to 5908.5 IU per day if you take a single 5000 IU vitamin D3 capsule along with a multivitamin with 400 IU of vitamin D3 and a calcium tablet with 400 IU of vitamin D3 as that is 5800 IU of vitamin D3 per day, very close to 5908.5 IU. Don’t be overly concerned about differences of less than 200 IU per day as frankly they are in the noise.
  8. Take your target dosage of vitamin D3 for 4 to 6 months, then retest and repeat steps 3 to 7 above to further fine-tune your vitamin D levels.

It’s OK to take your vitamin D every other day or even once or twice per week as it is fat-soluble and will accumulate in the body over time. Simply average out the amount you are taking over time to determine your average daily dosage. For instance, if take one 5000 IU vitamin D3 mini-softgel every other day, that works out to 17,500 IU per week or about 2500 IU per day. While it might be slightly better to take a consistent dose every day, this kind of variation should not be problematic and could save you a lot of money as 5000 IU softgels are often only slightly more expensive than 2000 IU softgels.

After these first two tests and adjustments, repeat a test once or twice per year to ensure that you are not straying far from your target level of vitamin D3. As long as you picked a 25(OH)D blood serum target somewhere near the middle of the optimal range, don’t worry about variations from your target of less than 5 ng/mL. Controlling results to that precision is not practical.

If you have a major change in lifestyle that affects your sun exposure or significantly alter your diet, you may want to recheck your vitamin D levels sooner. Examples of this are that you become a lifeguard at the beach after having worked in office buildings your whole life or that you strangely decide that cod liver oil (which has substantial amounts of vitamin D) is the ideal mix-in for your daily coffee or tea.

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Optimizing Vitamin D for Kids

Kids who cannot swallow vitamins are going to need vitamin D3 supplements in powder or drop form mixed into food or drink. Any kind of milk is a great drink to mix vitamin D3 as whether it is soy milk or cow milk, it has enough fat to dissolve the vitamin D3 well.

Vitamin D3 powders are very neutral tasting, so they can be mixed into other things, too. For instance, mixing vitamin D into mashed potatoes would probably work fine. Just do it after they have been cooked so that you’re not cooking the vitamin D supplements themselves.

It is likely that children approaching adult size, ages 16 and over, can use the same action plan as adults and it will work effectively.

Unless there are unusual circumstances, the same basic plan with lower dosages should work for younger children. Be sure to consult a pediatrician for advice for your child.

Children ages 6 to 16 can use a similar adjustment action plan, but start with a much lower dosage of 2000 IU per day for 7 days followed by 1000 IU per day for 60 days before doing a blood test. Kids that age are likely to spend time outside each day on the playground or playing sports, so they are going to get some vitamin D from sun exposure unless you amazingly manage to convince them to wear sunscreen on a regular basis.

You may get a very different number for the effect of vitamin D3 supplements upon blood serum 25(OH)D level for kids. For instance, considering their smaller size, you might get the result that it takes only 40 IU of vitamin D3 to change blood serum 25(OH)D by 1 ng/mL. In such a case, if you pick a target level of 60 ng/mL for 25(OH)D, then the child would need about 2400 IU per day of vitamin D3.

For children from 2 to 6, start with an initial dosage of 1000 IU per day followed by 400 IU per day for 60 days, then do the blood test to get the supplement vs. blood serum ratio and then adjust the supplement dosage.

For babies under 2 years old, ideally they will be breast-feeding. However, because so many mothers are vitamin D deficient, there is a significant risk the baby will not be getting enough vitamin D.

If the mother has solid vitamin D levels, the baby is probably going to be getting a reasonable amount of vitamin D through breast milk. The mother may need to add another 1000 IU to 2000 IU of vitamin D3 per day while nursing to ensure that her milk is rich in vitamin D for the baby. To be extra cautious, consider using vitamin D drops designed for babies such as Enfamil® D-Vi-Sol® Drops.

If the baby is feeding on formula, in the US it means the formula likely has enough vitamin D to ensure that the baby will be getting adequate vitamin D so long as he or she drinks 32 or more ounces (or about a liter) of formula per day. Look at the nutritional information on the formula to be sure about this. You can also supplement with vitamin D drops for these babies, too.

Babies ages 2 and under should be getting at very least 400 IU to 800 IU of vitamin D3 per day. Use the higher number for children who have darker skin, live far from the equator, and/or who don’t spend much time outside.

Dr. James Dowd’s book The Vitamin D Cure explains why people don’t get enough vitamin D, the health problems this causes, and how to improve health through vitamin D supplementation.


5 Stars! A mother of Dr. Dowd’s patient, June 4, 2009
By Val R (South Lyon (Detroit area), MI)

My son was lucky to be referred to Dr. Dowd when he was 13 years old. Dr. Dowd discovered he didn’t have rheumatoid arthritis (like his MD has suspected) or even “growing pains” like I suspected, but had low levels of vitamin D. After 4-6 weeks of vitamin D supplements, all his joint pain was gone! In addition, he stays much healthier (colds, flu, etc.) and much to our surprise, the warts on his feet finally went away…after three different doctors and three different methods of treatment for the warts!

Having the opportunity to meet Dr. Dowd is amazing. He is so smart and able to explain the immune system and the role of vitamin D in language even my 13 year old son could understand. Three years later, and my son is still symptom free as long as he keeps taking the vitamin D.

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Further Reading

Vitamin D Supplementation: Helpful or Hazardous?

Nutritional Problems May Lead to Higher Risk of Autism

Risk assessment for vitamin D

Vitamin D and Mental Illness

American Academy of Pediatrics: Vitamin D Deficiency Clinical Report

Pregnancy & Babies: Vitamin D

The Bioavailability of Vitamin D from Fortified Cheeses and Supplements Is Equivalent in Adults

These statements have not been evaluated by the Food and Drug Administration. The products mentioned in this post are not intended to diagnose, treat, cure or prevent any disease.

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  1. Varun
    October 1st, 2016 at 15:54 | #1

    Dear alison,

    I read your article(below) on optimising vitamin d. In the section “Action Plan for Optimizing Your Vitamin D3 Levels” i need your help please because my case is little different as i am suffering medicine interaction problem. I am taking magnesium as well & that’s the main problem. Magnesium interacts with every 2 nd medicine in this world & also with lots of herbs & foods. I was trying to find how my body levels went up & down with changing dosage but even after 1 year & 8-9 time blood tests i am unable to judge it because of the ongoing interactions of magnesium.


    So, Please tell a healthy adult optimisation figures like suppose if a healthy adult level is 47 nmol/l then with 1000 iu per day how much nmol/l per day will rise.

    I want to know a maintainance dose of vitamin d. Before supplementation my levels were 47 nmol/l. Please also tell is there any cure for magnesium deficiency(due to antidepressants) except supplements?

    Please help. I am waiting for it.

    Thank you,

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