Vitamin D is crucial for many functions in the body, but plenty of people are still deficient and most people have less than optimal levels. At the other end of the spectrum, some people are self-experimenting with huge doses of vitamin D. So what is safe, and what are the risks?
Given its vast array of uses within the body, vitamin D is codependent upon other vitamins and minerals, making it important not to supplement in isolation. This article provides a look at the other vitamins and minerals you should be augmenting alongside vitamin D, in order to safely reap the benefits for your super healthy beach body.
Vitamin D’s primary purpose is to facilitate mineral absorption (especially calcium), but it has a huge number of health benefits beyond that. Although it is called the sunshine vitamin, vitamin D is really a steroid hormone which influences many functions in the body, and is often prescribed as a treatment for dozens of health issues:
Vitamin D is used for conditions of the heart and blood vessels, including high blood pressure and high cholesterol. It is also used for diabetes, obesity, muscle weakness, multiple sclerosis, rheumatoid arthritis, chronic obstructive pulmonary disease (COPD), asthma, bronchitis, premenstrual syndrome (PMS), and tooth and gum disease. Some people use vitamin D for skin conditions including vitiligo, scleroderma,psoriasis, actinic keratosis, and lupus vulgaris. It is also used for boosting the immune system, preventing autoimmune diseases, and preventing cancer.
It has also been linked to protecting against prostate cancer  , strokes, heart attacks, tuberculosis, lung disease, clinical depression and Alzheimer’s Disease . In other words, these are all issues caused, allowed or exacerbated by people having low vitamin D levels, which is perfectly avoidable. Anything that can be ‘treated’ with vitamin D doses should probably never have occurred in the first place!
Vitamin D and longevity
There is a direct link between vitamin D levels and general risk of death [17,18,19]. Studies continue to show the link between vitamin D deficiency (measured by 25(OH)D blood serum levels) and all-cause mortality:
In this large cohort study, serum 25(OH)D concentrations were inversely associated with all-cause and cause-specific mortality. In particular, vitamin D deficiency [25(OH)D concentration <30 nmol/L] was strongly associated with mortality from all causes, cardiovascular diseases, cancer, and respiratory diseases.
Another study concluded:
In this meta-analysis of prospective, population-based cohort studies, a 20 nmol/l increase in 25(OH)D levels was associated with an 8% lower mortality in the general elderly population.
Vitamin D and muscle
One study  found a positive link between vitamin D and energy metabolism in muscle, which is of particular interest to anyone interested in building muscle or improving their athletic performance. Subjects who were extremely deficienct in vitamin D were supplemented with vitamin D3 (cholecalciferol) at roughly 8,500 IU per day:
Subjects were supplemented with cholecalciferol at adose of 60 000 IU/week for 12 weeks. MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr), phosphodiester (PDE) and ATP of the calf muscle were taken pre- and post-vitamin D supplementation. The study revealed significantly increased PCr/Pi ratio and decreased [Pi] and PDE/ATP ratio with raised serum 25(OH)D levels after 12 weeks of supplementation. The study indicates that serum 25(OH)D level plays an important role in improving the skeletal muscle energy metabolism and vitamin D deficiency might be one of the primary reasons for prevalence of low PCr/Pi ratio and high PDE values in normal Indian population as reported earlier.
Beyond the technical language, the study shows that energy metabolism in muscles is dependent upon vitamin D. Whether the benefits scale up once a deficiency has been rectified is still largely unknown. However, there is some evidence that athletic performance is improved when vitamin D levels in the blood are boosted beyond the ‘normal’ range of 30 ng/mL to around 50 ng/mL or more .
Another meta study , which is a study of other studies to provide a larger base of data, concluded that:
Vitamin D supplementation increases upper and lower limb strength
Vitamin D and fat loss
Yes, Vitamin D can also apparently assist with fat loss if you are deficient! A direct comparison of two groups of women, one given a placebo and one given 1000 IU/day showed a significant difference . On average, over the 12 weeks, the supplemented women lost 2.7 kg of fat, whereas the control group lost 0.47 kg fat. The average blood serum level of vit D at the start was 16.8 ng/mL, which is considered deficient.
Supplementation with vitamin D3 caused a statistically significant decrease in body fat mass in the vitamin D group compared to the placebo group (-2.7±2.1kg vs. -0.47±2.1kg; P<0.001).
Interestingly, although body fat was reduced, overall weight and size remained largely the same for both the supplemented and control groups, suggesting that the removal of vitamin D deficiency helps to maintain or even increase lean body mass.
A more recent study  went further and directly linked Vitamin D to a fat regulation role:
We showed that the VD3 supplementation limited weight gain induced by high-fat diet, which paralleled with an improvement of glucose homeostasis. The limitation of weight gain could further be explained by an increased lipid oxidation, possibly due to an up-regulation of genes involved in fatty acid oxidation and mitochondrial metabolism, leading to increased energy expenditure. Altogether, these data show that VD3 regulates energy expenditure and suggest that VD3 supplementation may represent a strategy of preventive nutrition to fight the onset of obesity and associated metabolic disorders.
Vitamin D and Cancer
A large scale study looking at the occurrence of breast cancer in women found that women who were deficient had over five times the risk those who had an optimal level of vitamin D:
Our present study has shown a significant association of low 25OHD levels with breast cancer risk such that women with the lowest levels of 25OH D (<50 nmol/L or 20 ng/mL ) had over five times the risk of breast cancer compared with those with the highest levels (>150 nmol/L or 60 ng/mL).
Although this is specifically about breast cancer, vitamin D has been linked to prevention and treatment of most types of cancer.
Vitamins D, K and A
Much of the advice and research on vitamin D fails to take into account its relationship with vitamin K (specifically K-2). There is a current belief that vitamin D is antagonistic to vitamin K-2, meaning that it causes the body to use up its K-2 stores as the vitamin D helps the body absorb more calcium and other minerals. We need the vitamin K-2 in order to activate matrix Gla proteins, also known as MGP, which tell the newly absorbed calcium where to be used.
If there isn’t enough K-2 in the body, it leads to calcification of the arteries as the calcium gets deposited in soft tissue [6,7]. This is why vitamin D toxicity is potentially really just a vitamin K deficiency. This theory hasn’t been properly explored yet though. The effect of using up vitamin K2 can be ameliorated using vitamin A supplementation along with vitamin D3 . You can find a much more in depth discussion here:
Overall, then, we see that both vitamins are needed for optimal health. Vitamin A alone did nothing to benefit the kidneys or the lungs. Vitamin D alone caused a remarkable reduction in the ability of carcinogens associated with cigarette smoke to induce lung cancer but itself caused kidney stones. When vitamin A was combined with vitamin D, lung cancer was improved just as much, and the kidney calcification was completely eliminated. Moreover, the activation of vitamin K-dependent proteins in the kidney was much stronger with both vitamins than with neither treatment, suggesting that the vitamin A not only “antagonizes” vitamin D toxicity in the kidney, but that the two vitamins synergistically improve kidney health.
This means that D, A and K-2 all work together. The question of ratios of A,D and K to ingest each day is very difficult because there simply isn’t any research into a suitable daily allowance of K2, or how A works in relation to D. Chris Masterjohn, the author of the above article suggests:
The truth is no one has any idea what the ideal intake of vitamin A is once you normalize vitamin D input to 2-4000 IU/day, but I suspect you want at least 1 or 2 times as much A as D in terms of IU.
Calcium, Magnesium and Zinc (and Boron)
One of the primary roles of vit D is to assist calcium absorption in the body. However, If you are planning to increase your D3 and K2 intakes, it might also be worth increasing your calcium intake to take full advantage of the benefits.
A further issue discussed by Chris Masterjohn is that high doses of vitamin D may cause a calcium deficiency by depleting the body’s store of calcium and actually removing some of it from our bones, highlighting the need for good sources of calcium:
Similarly, higher doses of vitamin D cause the body to use up its stores of magnesium. The Vitamin D Council suggests:
Magnesium may help vitamin D by helping your body activate vitamin D into a form your body can use, though it’s not known how much is ideal or if not getting enough magnesium harms your ability to fully make activated vitamin D. Also, magnesium is important in helping vitamin D to maintain calcium in the body and is essential for bone health.
Vitamins D and A have also been linked to increased plasma zinc levels , further highlighting the synergistic role that these two vitamins have in mineral ingestion in the human body. The Vitamin D Council suggests:
Zinc may help vitamin D to work inside the cells of your body. It’s also important in making sure that the calcium you get from foods or supplements is used in your bones. Vitamin D and zinc work together to strengthen your bones and to help them develop properly.
Luckily there are supplements that include all three of these minerals. Aim for one that includes copper too, since zinc and copper are antagonistic in the body. Another mineral worthy of mention is boron, which works with vitamin D to help your bones use the minerals they need, such as calcium. It has possibly been linked to increased testosterone when used with Vit D, Calcium and coconut oil .
However, there hasn’t been enough research to guarantee any substantial effect from increasing boron intake.
Vitamin D deficiency
A study of populations in central Europe  found that the average serum level was below 30 ng/mL, dropping to around 21-23 ng/mL during the winter months. These values are all regarded as ‘insufficient’, with a vast number of people falling into the ‘deficient’ category.
In the USA, the situation may actually be even worse. A study comparing 25(OH)D levels  from the 19988-1994 National Health and Nutrition Examination Survey and the same survey in 2001 to 2004 showed a strong decline in the average blood serum levels. During that period the average dropped from 30 ng/mL to 24 ng/mL.
Almost certainly, the hysteria around staying out of the sun and covering ourselves in sunscreen is to blame for this pandemic. Deficiency and insufficiency isn’t limited to those not taking supplements. Even people taking a multivitamin containing 400-600 IU/day are at risk of an insufficient level (under 30ng/mL), and most will still be under the current ‘optimal’ level of 50 ng/mL.
This is the danger of the false sense of security that a multivitamin can provide. As one blogger amusingly put it, the only way you aren’t deficient in vitamin D (if you aren’t taking a supplement) is if you:
- Get 15-20 minutes of mid-day sunshine on your bare skin without sunscreen most days during the summer, at a latitude not too far north or too far south.
- Do NOT wash with soap for the next 48 hours, so the vitamin D that formed on your skin can be absorbed into your bloodstream.
- During the winter, eat less (especially carbohydrates) so that you burn fat and provide your body with the vitamin D stored in that fat.
- Eat large amounts of yellow, orange, and red vegetables and fruits with dietary fat (to increase absorption) to get enough carotenoids (especially beta-carotene).
- Do NOT consume alcohol or smoke, as this will destroy carotene and prevent retinol (activated vitamin A) formation.
- Eat large amounts of green leafy vegetables and other source of vitamin K1 (also with fat, to increase absorption).
- Do NOT use antibiotics, which destroy the gut bacteria which convert vitamin K1 to vitamin K2.
Vitamin D toxicity (hypercalcemia)
Although it is extremely rare, vitamin D toxicity causes high levels of calcium to develop in your blood and arteries. High blood calcium is a condition called hypercalcemia. The symptoms of hypercalcemia include:
- feeling sick or being sick
- poor appetite or loss of appetite
- feeling very thirsty
- passing urine often
- constipation or diarrhea
- abdominal pain
- muscle weakness or pain
- feeling confused
- feeling tired
Toxicity is almost never observed at serum levels below 500 nmol/L (200 ng/mL), corresponding to oral intakes in excess of 20,000–50,000 IU/day. 10,000 IU/day can be taken, with considerable confidence, as the safe upper intake level. The criteria for efficacy depend upon the body systems evaluated. For calcium absorption, the system is not optimized until a level of 80 nmol/L (32 ng/mL) or higher is reached, and for fractures, falls, cancer, immune function, and insulin sensitivity, the efficacy criterion is less well established, but is at least as high as for calcium absorption, and perhaps as high as 120 nmol/L (48 ng/mL).
Neither of those safety reviews of vitamin D include a single mention of the role that vitamins A and K may play in preventing/causing toxicity, and only focused on D supplementation in isolation.
Potentially, with proper combined supplementation, the upper tolerable levels of vitamin D intake could be much higher but we won’t know until the research finally catches up. It should also be noted that single doses of up to 600,000 IUs have been safely provided by the Mayo Clinic:
For deficiency, at least 1,000 IU (25 micrograms) of vitamin D has been taken by mouth daily (or 8,400 IU of vitamin D3 weekly). Other doses that have been studied include 50,000 IU daily for six weeks, 300,000 IU of oral vitamin D3 three times a year, 800 IU daily in combination with calcium, 400 IU daily, and 300,000 IU every three months. 300,000 IU of vitamin D has been used intramuscularly as a bolus dose of vitamin D2 or D3, three times per year, and 600,000 IU (15 milligrams) of vitamin D has been used as a single injection.
One famous case of vitamin D toxicity was Gary Hall, who managed to accidentally overdose on 2,000,000 IU/day… using his own health product!
Self-experimentation with high doses
There are (unresearched) claims of very high doses actually fixing long term health issues. In his book about self experimentation, Jeff Bowles claims that a year on high doses (20-100,000 IU per day) cured his bone spurs, hip clicking, cysts, toenail fungus, joint popping/cracking and… the common cold. He also believes that it probably caused him to lose body fat when he reached levels of 40,000 IU per day.
Other groups are also self experimenting with doses up to 50,000 IU per day. The problem with high doses is that there are many factors determining how well a body copes, and everyone is different. Diet, supplements, age, sex, size, body fat, genes and many other factors make it impossible to say for sure where the upper tolerable limit for an individual may be.
This is why experimenters start low and slowly build up their intake, along with regular blood tests to keep an eye on their serum levels and to check for any strain on the kidneys. There was a reported fatality in the 1930s of a scientist attempting to replicate a previous claim of vit D curing arthritis by taking 2,100,000 IU/day of D2 (the less potent form) for 18 days. This dose was taken in isolation, without any supporting supplements such as vitamins A or K.
The vitamin D council advises against high doses without extreme care:
When I hear of people taking 50,000 IU per day I worry. Everyone is different in how they metabolize vitamin D. Some people can tolerate 50,000 IU per day and some people can’t. By the time you realize you are in the latter category, it may be too late. Make sure to follow the Council’s guidelines for adults of 5,000 IU/day, at the most 10,000 IU/day, as 10,000 IU/day is the no observed adverse effects level (NOAEL) of the 2010 Food and Nutrition Board, the amount that has never been shown to cause harm. Do not exceed 10,000 IU/day unless you have a scientific level of understanding of vitamin D metabolism and test often.
Vitamin D blood serum levels
Vitamin D levels in the blood are monitored by measuring 25-hydroxy-vitamin D levels, usually written as 25[OH]D , although the terms are largely used interchangeably. The test can be done relatively cheaply, and it is worth getting one done, especially if you are potentially low or aiming for a high dose supplementation.
|ng/mL||Vitamin D status|
|below 10||Severely deficient|
These numbers are based on an amalgamation of the general guidelines available. As you can see, you should be aiming for at least a 50 ng/mL serum level, with a very high margin of safety above that amount. The 50-60 ng/mL range was found in a study of athletic performance :
Vitamin D may improve athletic performance in vitamin D-deficient athletes. Peak athletic performance may occur when 25(OH)D levels approach those obtained by natural, full-body, summer sun exposure, which is at least 50 ng x mL(-1). Such 25(OH)D levels may also protect the athlete from several acute and chronic medical conditions.
It also turns out that 50 ng/mL is also roughly the level where some vitamin D begins to be stored in our body fat, suggesting that it is no longer in a state of deficiency as judged by the body’s own internal monitoring. According to the Vitamin D Council newsletter:
It turned out that the body does not reliably begin storing the parent compound (cholecalciferol) in fat and muscle tissue until 25(OH)D levels get above 50 ng/mL (125 nmol/L). The average person starts to store cholecalciferol at 40 ng/mL (100 nmol/L), but at 50 ng/mL (125 nmol/L), virtually everyone begins to store it for future use. That is, at levels below 50 ng/mL (125 nmol/L), the body is usually using up the vitamin D as fast as you make it or take it, indicating chronic substrate starvation, not a good thing.
It is worth noting the huge gap between 60ng/mL and 200 ng/mL. This is as far as the research has made it so far and we don’t yet know if a level of 120ng/mL might actually be optimal, for example.
Vitamin D dosage
Most supplements are now vitamin D3 (cholecalciferol). Vitamin D2 (Ergocalciferol), the other main version, is generally considered a much inferior version for supplementation but is still available in places like the US so check the label before you buy; you want D3 cholecalciferol. Currently, the recommended DV (Daily Value) set by the FDA for D3 is 400IU.
According to the Institute of Medicine, the RDA (Recommended Dietary Allowance) is 600 IU per day. In the UK, the NHS hasn’t set an RDA, but recommends that:
If you take vitamin D supplements, do not take more than 25 micrograms (1000 IU) a day, as it could be harmful.
There is no medical evidence of anything less than 40,000 IU/day being harmful.
Many health professionals would suggest that the minimum should be closer to 800-1000 IU per day. For example:
Historically, 400 IU (10 ug) of vitamin D was recommended for better health because it closely approximated the amount of vitamin D in a teaspoonful of cod liver oil. However, 800 to 1,000 IU is the dose that may have a better chance of giving a patient a normal vitamin D level.
I am not sure what the merit of suggesting anyone aims for a ‘normal’ level of vitamin D is; surely aiming for optimal levels is always desirable?
The Endocrine Society has suggested an upper level of 4000 IU per day, with up to 10,000 IU per day to correct a deficiency.
Vitamin D Peak Health Dose
For anyone looking at a peak health dose, I would suggest that 4,000 IU should be where you start. As an extremely rough estimate, 4000 IU per day should allow you to raise your serum level by around 40 ng/mL, which should put you close to the optimal level of 50-60 ng/mL when combined with a bit of sun and food intake.
If you are seeking to increase your vitamin D, bear in mind that it can take from three weeks to three months of supplementation for blood levels to reach the desired level.
Focus on the blood serum levels, not the IU
Rather than concentrating on the amount of IU you are getting daily, you should focus on attaining a specific blood serum level such as 60 ng/mL.
The amount of vitamin D needed to achieve this varies enormously from person to person, and will depend on diet, age, sex, ongoing illness, body fat, metabolism, and so on.
The easiest way to do this is begin with a base level of 4000 IU/day for a couple of months and then get a blood serum test. This should give you an indication of how much more, or less, you need to take, using the following as an approximate guide (don’t forget to retest after three months):
- 500 IU (12.5 mcg) per day increases vitamin D blood levels 5 ng/ml (12.5 nmol/L).
- 1000 IU (25 mcg) per day increases vitamin D blood levels 10 ng/ml (25 nmol/L).
- 2000 IU (50 mcg) per day increases vitamin D blood levels 20 ng/ml (50 nmol/L).
Take vitamin D supplements with your main meal
Although the labels on supplements suggest taking vitamin D with food, they don’t make enough effort to inform you of just how important this is. Patients seen at the Cleveland Clinic Foundation Bone Clinic for the treatment of vitamin D deficiency were asked to switch to taking their dose with the main meal of the day , resulting in an average serum 25(OH)D level increase of 56.7%:
Thus it is concluded that taking vitamin D with the largest meal improves absorption and results in about a 50% increase in serum levels of 25(OH)D levels achieved. Similar increases were observed in a wide range of vitamin D doses taken for a variety of medical conditions.
This is because vitamin D is fat soluble, and the main meal will contain the largest amount of fat, thus helping with absorption.
A similar study  showed a distinct difference of absorption for a 50,000 IU dose given to people also taking in 15 grams of fat or more at the same time, compared to others taking in 0 grams of fat. 15 grams of fat is roughly equivalent to a tablespoon of olive oil or MCT oil.
Can I get enough from sunlight?
It is possible to get a good dose of vitamin D from sunlight or a UVB tanning bed, and there is no evidence of it being possible to produce toxic levels from sunbathing. A 21-year-old man or women exposed to summer UVB light generates around 10,000-25,000 IU of vitamin D in 15 to 20 minutes, assuming a large skin surface being exposed (i.e. sunbathing) and assuming that the sun is hot enough.
However, longer exposure does not produce more vitamin D (it reaches a saturation point) and there is evidence that washing your skin after sunbathing actually washes off some of the vitamin D formed in the outer skin layer. Hence, dipping into the swimming pool regularly, or showering, will significantly reduce the vitamin D benefit from your sunbathing.
The other issue with sunbathing for vitamin D is that the sun isn’t consistently shining every day! In the UK, for example, the sun makes an appearance for a weekend, known locally as ‘the summer’, and then disappears for another year. That’s not going to provide enough sunlight, especially in winter.
Vitamin D in food
In terms of food, there are some sources but they contain relatively little vitamin D, and certainly not enough for maintaining an optimal level. According to the NHS, ‘good’ food sources are:
- oily fish, such as salmon, sardines and mackerel (around 1000 IU per whole wild salmon)
- eggs (87 IU per egg)
- fortified fat spreads
- fortified breakfast cereals
- powdered milk
Vitamin D is fat soluble, so you need to eat oily fish, including the skin, to get the benefit. Farmed fish contain just 25% of the vitamin D of wild fish. A study of vitamin D in fish concluded:
However, our analysis of the vitamin D content in a variety of fish species that were thought to contain an adequate amount of vitamin D did not have an amount of vitamin D that is listed in food charts.
It is hard to recommend just relying on food and sunshine for your vitamin D, since you will probably end up with insufficient levels, and are very unlikely to achieve optimum levels.
Vitamin D high doses
Despite the scaremongering around vitamin D toxicity, it is actually very rare to find a case of toxicity other than in cases of accidental overdosing or those with an existing illness. Unfortunately there has been little research done into the safe/optimal upper levels of vitamin D, and nothing when vitamins A and K-2, plus minerals, are also supplemented. One study of interest  that actually used high doses concluded this:
Patients’ serum 25(OH)D concentrations reached twice the top of the physiologic range without eliciting hypercalcemia or hypercalciuria. The data support the feasibility of pharmacologic doses of vitamin D3 for clinical research, and they provide objective evidence that vitamin D intake beyond the current upper limit is safe by a large margin.
Note that the multiple sclerosis patients, over 28 weeks, were given 1200 mg Calcium per day along with progressively increasing doses of vitamin D3: from 4000 to 40,000 IU per day. That is ten times the suggested safe upper limit, without vitamin K or A supplementation, resulting in no toxicity. That’s no surprise, since the human body is capable of comfortably handling 10-25,000 IU per day just from sunbathing.
However, if you are tempted to self experiment, I would definitely suggest taking a mixed vitamin K supplement and a vitamin A supplement too, and have your serum levels tested regularly.