What Is Vitamin D Good For? Health Benefits & Overdose Toxicity,
Growing up, parents, teachers and doctors probably told you time and again how important it was to drink your orange juice to get your vitamin C.
But how often do you remember them telling you that you also needed to get your vitamin D?
Vitamin D has been largely overlooked in the public eye, and doesn’t really get the attention it deserves.
But all of that is starting to change.
As researchers learn more and more about what vitamin D can do for you, the spotlight is finally starting to shine on this vital nutrient.
In this article, I will share some of the studies which have been surfacing so that you too will understand the many benefits of vitamin D.
But first, let’s talk a little bit more about what vitamin D is, how much vitamin D you need, and how you can boost the amount of vitamin D you are getting in your diet.
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What is Vitamin D?
Vitamin D is often referred to as the "sunshine vitamin." That is because your skin manufactures it when exposed to the sun.
That is not the only source of vitamin D.
You also can get vitamin D through your diet (though this is hard to do), and you can take vitamin D supplements (which you probably should be doing - more on that shortly).
Curiously enough, vitamin D is not really classified as a vitamin. Also referred to as "provitamin D," it is actually a precursor to a steroid hormone.
Vitamin D has to be converted before it can be used in the body. This takes place initially in the liver and kidneys.
Only after this process takes place is it in a biologically active form, known as "calcitriol."
Vitamin D has numerous important functions in the body, and can impact hundreds of genes (1).
Because of this, vitamin D is essential if you want to prevent a range of adverse health conditions.
Vitamin D shares a close relationship with another important nutrient, and that is calcium.
Your body requires vitamin D in order to metabolize and maintain your calcium levels.
That means that supplementing with vitamin D may help to boost your calcium levels.
Vitamin D also is involved with the parathyroid.
Without enough vitamin D, your parathyroid goes into a hyperactive state, which in turn results in low phosphorus levels in your blood.
Phosphorus is required in order for calcium to mineralize in your bones.
That means that vitamin D is not only vital for maintaining calcium levels, but also for converting calcium into healthy bone tissue.
Vitamin D Deficiency is Surprisingly Common
You might think that a vitamin which is available through simple exposure to sunlight would be easy to come by.
But the reality is that a lot of people do not get nearly enough vitamin D in their diets to function optimally.
In areas which are prone to weeks of cloudy days at a time such as the Pacific Northwest, many people simply do not get enough sun exposure.
This is something I know about from experience.
My friend is a resident of the Oregan who have had multiple doctors talk to him about taking vitamin D supplements.
This is something which they routinely tell all their patients, because they know that their levels are sub-par due to the climate.
Also keep in mind that this may also be relevant if you live in a cold climate, and thus tend to cover up even when it is sunny out.
It may be an issue as well in any sun-drenched climate (ironically) if you wear a lot of sunscreen or avoid going outdoors to keep from getting burned.
Many people in today’s world also do not get outside because of their work hours.
If you work a 9-5 job and you do not have a window nearby, you may get little or no sunlight during the day.
This is also something I know about from experience. I once worked in a store which was located in the basement of a ski resort in Colorado.
I arrived before the sun rose and left after it set each day, so I literally saw no sunlight except on the weekends.
I also clearly remember growing up how many of our classrooms at school had no windows.
Many of the staff also had no sun exposure during their days.
Another thing you may not know about vitamin D deficiency is that some people have a higher risk for developing it than others.
On average, the risk is 41.6%, but if you are Hispanic, your risk is 69.2%, and if you are black, it is 82.1% (3).
There is a significantly higher risk as well for those who are elderly (4).
If you have a health condition, there may also be a chance your risk is higher.
For example, an astonishing 96% of heart attack patients have been shown to be deficient in vitamin D (5).
Have an iron deficiency? This is another health condition which can impact vitamin D levels in your body by hindering absorption.
You may be familiar with the bone disease known as rickets.
If the name sounds a bit archaic, that is because rickets has largely been wiped out in the west (6). This is thanks to fortification in food.
If you end up with vitamin D deficiency, you could be putting yourself at a heightened risk for osteoporosis (7).
Other possible consequences could include cancer, multiple sclerosis, dementia, diabetes or heart disease (8).
KEY POINT: While you might think you are getting enough vitamin D, there is a good chance you are deficient if you live in a cloudy climate or you work in a windowless environment.
How Much Vitamin D Do You Need? (Dosage)
According to the National Institute of Health (2), you need the following amounts of vitamin D each day based on your age:
- Birth to 12 months - 400 IU
- Children 1–13 years - 600 IU
- Teens 14–18 years - 600 IU
- Adults 19–70 years - 600 IU
- Adults 71 years and older - 800 IU
- Pregnant and breastfeeding women - 600 IU
Why is it so hard to get this much vitamin D without taking supplements?
Because not a lot of foods contain it. I will provide some recommendations shortly.
One more thing that you should note is that it is possible that the recommended daily amount of vitamin D may itself be too low.
KEY POINT: If you are an adult, you need around 600 IU of vitamin D every day.
It is hard to meet this requirement through diet and sun exposure alone.
Can You Get Too Much Vitamin D and Overdose?
Yes, it is possible to get too much of a good thing.
If you take too much vitamin D, you may experience toxic effects such as constipation, vomiting, nausea, loss of appetite, weight loss and weakness.
Furthermore, you may also experience heart arrhythmia, confusion and disorientation.
Kidney damage is a risk as well.
Here are the upper limits for daily vitamin D as recommended by the National Institute of Health:
- Infants: 1,000-1,500 IU
- Children aged 1-8: 2,500-3,000 IU
- Children age 9 and older along with all adults: 4,000 IU
It is worth noting however that these are not really "hard" limits.
Indeed, the Food and Nutrition Board, which set these limits, has also stated a "No Observed Adverse Effects Level (NOAEL) of 10,000 IU/day for adults."
This means that there are no studies published which indicate that 10,000 IU/day produces any adverse effects.
In other words, 4,000 IU is not really the maximum limit. You can take 10,000 IU every day without a problem if you need to.
This makes sense, considering you can get this amount just from sunlight (49).
Of interest is this study (50) in the International Journal of Endocrinology in 2013.
The researchers wanted to find out how much vitamin D supplementation was needed to achieve the 25(OH)D serum level above 30 ng/mL in order to treat various conditions.
The scientists prescribed vitamin D in multiples of 25,000 IU to different groups.
Even these high doses did not result in the target serum level for all the participants.
The researchers concluded, "Thus, if a 25(OH)D level of 30 ng/mL or more is targeted in future studies, higher doses than the IOM Upper Limit should be used."
This study also lends credence to the idea that more than 4,000 IU is acceptable - and in some cases, perhaps even necessary if a patient must achieve a certain serum level.
Note that you cannot get too much vitamin D just from exposure to the sun.
The only way you are likely to overdose on vitamin D is if you are overdoing it with your supplementation.
But this is also unlikely so long as you are taking reasonable amounts.
Indeed, vitamin D toxicity is not a common event.
It is generally a cumulative effect of taking excessive amounts of vitamin D over an extended time period.
This condition is referred to as "hypervitaminosis D."
The reason that vitamin D may build up in the body is that it is fat-soluble, rather than water-soluble.
If this does happen, the vitamin D behaves in a manner similar to how a steroid would.
If you end up with a toxic build-up of vitamin D, there is a significant amount of free vitamin D floating around.
This free vitamin D can activate or deactivate various genes in your cells.
This can result in an increase in the absorption of calcium from the foods you eat (53).
If that excess calcium binds to your kidneys and other tissues in your body, it can result in damage to those organs and systems.
Further symptoms include nausea, vomiting, constipation, diarrhea, weakness, and excessive thirst (63).
So how much is really too much?
It can take months of build-up before symptoms of toxicity are noticeable, but damage may occur even without symptoms.
Blood tests can detect kidney failure and hypercalcemia markers even before the patient feels ill (64).
So if you are taking excessive amounts of vitamin D and still "feel fine" after a few months, it does not mean you are fine.
If you are taking large amounts of vitamin D and want to reduce your chances of developing a toxic reaction, taking vitamin D in conjunction with other fat-soluble vitamins may be helpful.
Vitamin A is also important, as it can protect vitamin K stores.
KEY POINT: If you overdose on vitamin D supplements, you can develop an adverse and dangerous reaction.
Thankfully this is a rare occurrence, but it has been seen at doses between 40,000-100,000 IU.
While the recommended daily upper limit is just 4,000 IU, the NOAEL is 10,000 IU.
And in some cases, 4,000 IU may not be sufficient to raise serum levels to the targeted amount.
So some patients may want to take more than 4,000 IU in certain cases.
If you have any doubts about your safety, always consult with a medical professional.
How to Increase the Vitamin D in Your Diet
Dietary vitamin D comes in two main forms:
- Vitamin D2: Ergocalciferol (from plants).
- Vitamin D3: Cholecalciferol (from animals).
The animal form (D3) increases blood levels much more effectively than D2 (72).
Here are some foods you can eat which contain significant amounts of vitamin D.
This information again comes from the fact sheet from the National Institute of Health:
As you can see, this is not an extensive list, which is why it is so hard to get adequate vitamin D just through diet.
While you can (and should) spend some time out in the sun to get more vitamin D, you need to make sure you are not doing so excessively, as exposure to UV rays can have a very harmful effect on the body (12, 13).
Again, this is why you probably will need to take vitamin D supplements if your levels are low.
KEY POINT: There are a few foods and beverages which contain significant levels of vitamin D, but for the most part, you cannot rely on dietary sources.
16 Health Benefits of Vitamin D
Now that you know more about vitamin D and the pervasiveness of vitamin D deficiency, let’s check out some of the many vitamin D benefits which are currently backed by scientific research.
1. Vitamin D can reduce your chances of heart disease.
Heart disease is still the most common cause of death around the globe, so anything you can do to protect the health of your heart and cardiovascular system is important.
Multiple observational studies have shown that if your vitamin D levels are low, that may lead to an increased risk of heart attack.
KEY POINT: If you want to reduce your risk of heart disease, there are some observational studies which indicate that taking more vitamin D may help.
2. Vitamin D can reduce the likelihood of developing multiple sclerosis.
Another disease which adequate vitamin D intake may be able to help prevent is multiple sclerosis.
Multiple sclerosis (MS) is an autoimmune disease which can have many severe effects, including loss of vision, pain, coordination impairment, and fatigue.
Research is still in the early stages however, so more is needed to confirm whether this is indeed the case.
KEY POINT: Initial research on vitamin D and multiple sclerosis is promising.
It is possible that maintaining adequate vitamin D levels could prevent the disease or slow its progression.
3. Vitamin D can help combat the flu.
Looking for a natural remedy during flu season?
While there are a lot of supplements which are promoted as preventatives or treatments for the flu, not a lot of them are backed by scientific evidence.
One which is however is vitamin D. In one study (23), students receiving vitamin D had a significant reduction in influenza infections.
KEY POINT: If you take vitamin D during flu season, you may be less likely to come down with the flu.
4. Vitamin D can reduce your risk of asthma attacks.
The same study on schoolchildren above which looked at influenza also looked at asthma.
Researchers noticed that far fewer children who took vitamin D and had a previous diagnosis of asthma suffered a subsequent attack than those who took the placebo.
KEY POINT: It is possible that taking vitamin D not only can fight the flu, but also prevent asthma attacks.
5. Your overall risk of mortality drops when you take more vitamin D.
In fact, that second study linked above included data from 94,148 participants across fifty randomized trials.
Both studies found that taking vitamin D significantly reduced the overall risk of death by up to 7%.
This is likely because low vitamin D intake has been linked to a number of lethal conditions such as diabetes, cancer, and heart disease.
These conditions together account for up to 70% of deaths in high-income nations.
By taking more vitamin D, participants in the study who supplemented most likely reduced their chances of developing these diseases, which is why their overall death rates were lower.
KEY POINT: Research indicates that your overall likelihood of death from a variety of causes drops if you supplement with vitamin D.
6. Vitamin D can reduce your chances of developing cancer.
Cancer is currently among the most pervasive and deadly diseases on the planet, and there is no sure way to prevent, treat, or cure it.
As such, anything which you can take which can possibly help you out is worth your while.
One of the more promising supplements for possibly preventing cancer is vitamin D.
Furthermore, in 2008, there was a fascinating intervention study (33) to address the gap in research (as the majority of studies in this area are observation).
The study spanned a period of four years and was double-blind, randomized, and placebo-controlled. 1,179 subjects participated in all.
The subjects who took 1,100 IU of vitamin D3 together with calcium were found to have a 60% less chance of developing cancer than those who did not take the supplement.
More research is needed to say anything definitive about cancer and vitamin D, but for now, there is reason to be optimistic.
Because cancer is such a huge risk (the lifetime risk is 38.5%), anything you can do to try and reduce that risk is very important.
KEY POINT: While there are a lot of supplements which are talked about in the area of cancer prevention and treatment, one of the few that actually has some science backing it up is vitamin D.
More research is needed to say for certain that vitamin D does effectively prevent cancer, but for the time being, it looks like it may be one of your more hopeful options.
7. Taking high dosages of vitamin D may be able to help stave off depression and/or anxiety.
There has been some research into vitamin D and mental illness.
In one study (34), the effects of vitamin D on depression in overweight participants was examined in a double-blind, randomized trial.
The researchers discovered that there was a correlation between depression symptoms and serum levels of vitamin D.
Furthermore, they found that participants who took vitamin D in high dosages experienced a reduction in symptoms.
Another interesting study (35) examined anxiety and depression in patients suffering from fibromyalgia.
The researchers noted that vitamin D deficiency commonly occurs in patients with this disease, and that it is most prominent in those who also experience depression and anxiety.
So this is a further suggestion that insufficient vitamin D may contribute to mental imbalance.
KEY POINT: Scientists have found that low vitamin D levels are associated with depression and anxiety, and furthermore that taking high dosages of vitamin D may help to alleviate symptoms.
8. Taking vitamin D in conjunction with calcium may help you to lose weight.
Indeed, the researchers stated that, "During the weight-reducing programme, a calcium+D supplementation was necessary in female overweight/obese very low-calcium consumers to reach significant fat mass loss."
The word "necessary" here stands out. In short, not only was the vitamin D+calcium combination helpful, it was vital to achieving significant success.
The researchers believed that the explanation for the effectiveness of this treatment had to do with a decline in lipid intake.
This in turn may have been a result of the supplement reducing appetite.
KEY POINT: If you want to lose weight quickly, it helps to suppress your appetite so that you are less tempted to overeat.
Taking vitamin D plus calcium may enable you to do this effectively.
9. Vitamin D reduces the chances of developing childhood type 1 diabetes.
There are multiple studies which show that children who take vitamin D supplements may have a lower risk of developing type I diabetes.
In a study (37) of 10,821 infants, it was found that "dietary vitamin D supplementation is associated with reduced risk of type 1 diabetes."
By taking 2000IU a day, the reduction in risk was as much as 78%.
In another meta-analysis (38), the same conclusion was reached.
Taking vitamin D during early childhood may have a protective effect against type 1 diabetes.
The reduction in risk was 29% and dose dependant.
Since most of the research (49) out there is currently observational, randomized controlled trials are needed in order to make a more solid determination about the effectiveness of the treatment.
KEY POINT: Vitamin D supplementation for infants may help to prevent type I diabetes, but more research is needed to be conclusive about it.
10. Vitamin D reduce the chances of adult type II diabetes.
Just as vitamin D may help to reduce the risk of type I diabetes in children, it may actually do the same for adults when it comes to type II diabetes.
This study (39) analyzed the relationship between type 2 diabetes and vitamin D by looking at other research trials and observational studies.
It was discovered that in two trials, supplementing with vitamin D helped to improve insulin resistance.
It was also found that those participants who had the highest levels of vitamin D had overall a 43% reduced risk of type 2 diabetes compared to those with the lowest levels.
The researchers concluded that vitamin D may help to stave off type 2 diabetes, but that more trials are needed in order to say for sure whether that is in fact the case.
KEY POINT: Early research into type 2 diabetes and vitamin D indicates that supplementation may help to reduce risk for the disease.
11. Taking vitamin D can help to prevent fractures and falls in old age.
You already know that if you do not get enough vitamin D, you are at an increased risk for developing osteoporosis.
In order for the supplement to be effective toward this end, you need to take at least 800 IU daily.
Doses as low as 400 IU had no measurable impact on the instances of fractures and falls.
KEY POINT: Studies have shown that vitamin D supplementation at doses of 800 IU or higher can help to reduce fractures and falls among the aging population.
12. Vitamin D can possibly improve the prognosis for leukaemia.
I have already talked a bit about how vitamin D may be helpful in preventing cancer.
But some specific research has been done in the area of leukaemia.
It has been discovered (43) that vitamin D insufficiency is indeed associated with the condition.
Researchers still do not know whether supplementing with vitamin D could improve the prognosis for leukaemia, but it certainly warrants additional testing.
KEY POINT: It is possible that taking vitamin D to treat insufficiency could also led to a better prognosis in cases of leukaemia.
13. Vitamin D can possibly prevent cognitive decline and dementia.
Cognitive impairment and dementia are swiftly on the rise.
The World Health Organization reports that about 47 million people have dementia, and that by the year 2050, that number will triple.
Those are frightening statistics, and right now, there is no single supplement which researchers are sure can significantly reduce your chances of getting Alzheimer’s or another form of dementia.
A lot of research is needed to establish whether supplementing with vitamin D could help to prevent dementia.
Nonetheless, it seems logical that it would, since it would help you to maintain normal, healthy levels.
This in turn should reduce your overall risk profile, hopefully preventing cognitive decline and keeping your mind sharp over the years ahead.
KEY POINT: Since cognitive decline is associated with low levels of vitamin D, supplementing regularly with D may be helpful in maintaining cognitive health and preventing dementia.
14. Treat osteoporosis by taking vitamin D in conjunction with calcium and sodium fluoride.
One treatment which is sometimes given to patients with low bone mass in order to develop new bone tissue is sodium fluoride.
Unfortunately, this treatment is not entirely effective since the bone which is created through it is not well-mineralized.
For this reason, studies have been conducted to see whether sodium fluoride is more effective when taken with calcium and vitamin D (46).
It was found that this treatment helps to prevent osteomalacia (bone softening) and secondary hyperparathyroidism (an adverse hormone condition) during bone formation.
KEY POINT: Taking vitamin D and calcium along with sodium fluoride may make for a more effective treatment for osteoporosis.
15. If you are an athlete, taking a vitamin D supplement may help you steer clear of problems associated with D deficiency.
Many athletes are deficient in vitamin D.
Unfortunately, vitamin D deficiency can pose some safety concerns for athletes.
Because a lack of vitamin D weakens bone structure, athletes who are deficient in it may be more prone to stress fractures.
Additional symptoms which are common among vitamin D deficient athletes include illness and musculoskeletal pain.
If you are an athlete, taking vitamin D supplements may help you to avoid these problems (47).
This can keep you safe during your workouts while also reducing pain and sickness.
KEY POINT: Athletes with vitamin D deficiency may experience fractures, illness and pain.
Supplementing with vitamin D can prevent all these problems.
16. Vitamin D can possibly boost the results of your workouts.
You now know that athletes can benefit from vitamin D supplementation because taking vitamin D can prevent deficiency-related symptoms.
But vitamin D also has benefits in the areas of protein synthesis, electrolyte metabolism and gene expression (48).
This means that it may help athletes to improve their performance and increase muscle strength.
Further research in this area is required in order to determine if this is indeed the case.
KEY POINT: Athletes may also experience benefits in the area of performance if they supplement with vitamin D.
How to Shop for Vitamin D Supplements
Now that you know all about the health benefits of vitamin D, you hopefully are ready to shop for vitamin D supplements.
Here is what you should be looking for when you are shopping:
There are other forms of vitamin D out there, but vitamin D3, also known as “cholecalciferol,” is the same form of vitamin D manufactured in your own body in response to sunlight.
Naturally this type of vitamin D is most useful to your body.
It is always best to buy organic supplements when you can which contain safe, healthy, all-natural ingredients.
No additives or fillers
Stay away from vitamins which have a lot of unwanted fillers which may not be great for your health.
Manufactured according to FDA standards and independently tested
This is ideal to ensure that you are getting the quality you are paying for.
Easy to swallow and digest
If you have a hard time swallowing pills, check reviews for the product you are considering to see if others had an easy or difficult time with the vitamin D you are thinking of purchasing.
The right dosage for your needs
How much you need will depend on what you are trying to prevent or treat, where you live, and whether there are any other risk factors for deficiency you need to worry about (age, etc.).
Consider shopping for vitamin D plus calcium
As you probably noted while reading through the studies I have cited, vitamin D and calcium together have been shown to be an effective combination.
This is especially relevant in certain situations, for example if you are trying to lose weight or prevent cancer.
The best value
The best value for a vitamin D supplement is not necessarily the least expensive product overall - it is the one which gives you the lowest cost per count and which provides you with a pure, potent supplement for your health.
Looking for recommendations? Check out our Vitamin D Buying Guide.
KEY POINT: When you are shopping for vitamin D, stick with vitamin D3 supplements rather than other forms such as vitamin D2 which you may also encounter.
Weigh quality, ingredients and cost as other important factors so that you can choose the best product.
Conclusion: Vitamin D Is Vital for Your Overall Health, and You Probably Are Not Getting Enough Of It
With its potential benefits for bone health, cancer prevention, protection against heart disease, and more, vitamin D is an excellent supplement for supporting your overall health.
Vitamin D is also a nutrient you may very well not be getting enough of, even if you live in a first world country.
Since diet alone is not an adequate source, and you also may have a hard time getting enough vitamin D through sunlight, it is very important to take the "sunshine vitamin" in supplement form.
Be sure to check out our recommended vitamin D supplements (coming soon) so that you can stay healthy now and in the future!
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