Amount of Evidence: Very High Potential Benefits: Very High Safety: High
TABLE OF CONTENTS
What is vitamin D?
This fat-soluble essential vitamin is one of the most popular supplements on the market and for a good reason. It is most commonly taken to support the immune system and improve bone health. However, these are just two of the many potential benefits of vitamin D. In this article, we will look at vitamin D’s main benefits, potential side effects, and how to use it the right way.
Potential benefits
It is important to note that all of the potential benefits mentioned below are dose-dependent. In general, the higher the dose you take, the more pronounced the effects will be. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Major benefits
Correcting a vitamin D deficiency – A severe vitamin D deficiency can have a terrible impact on health and overall quality of life. The symptoms of vitamin D deficiency include mood swings, depression, poor bone health, high blood pressure, multiple sclerosis, severe asthma in children, poor immune system functioning, and much more. If you experience some of these or you know your vitamin D levels are too low, taking the supplement is almost a must.
Reduced Covid-19 severity – Vitamin D3 appears to be the most effective nutritional supplement for reducing the severity of covid-19. The difference between those who have optimal levels of the vitamin and those who don’t is significant in this regard. The supplement appears to be more effective for improving immune health than nearly any other supplement on the market.
Reduced risk for cancer – Getting to your optimal vitamin D levels reduces the risk for colorectal cancer by around a half. The supplement has also been shown to reduce the risk for some other types of cancer, such as breast and pancreatic cancer, to some degree.
Improved bone health – Vitamin D supplements have been shown to reduce bone fracture risk and increase bone mineral density at doses of 800 IU or more.
Reduced all-cause mortality – Those with optimal levels of vitamin D live longer than those with suboptimal levels. The vitamin slows down aging by keeping your telomere length normal.
Minor benefits
Reduced symptoms of depression – The scientific evidence to support this effect is not strong. However, there is a lot of anecdotal evidence showing that the supplement can significantly reduce the symptoms of depression if you are deficient in vitamin D.
Improved calcium absorption – This effect is directly responsible for many of the other benefits. Fixing your vitamin D deficiency and getting to the optimal blood level significantly improves calcium absorption. However, if you further increase vitamin D levels beyond the optimal levels, no additional increase in calcium absorption will happen. The supplement also doesn’t have a notable effect on plasma or serum calcium levels.
Reduced severity of viral infections – The supplement can be useful for reducing the symptoms of the common cold, flu, and some other types of sickness. This effect is not as powerful as the supplement’s effect on reducing the symptoms of covid-19 though.
Improved insulin sensitivity – Vitamin D increases pancreatic insulin secretion, which leads to an improvement in insulin sensitivity. This benefit applies primarily to type 2 diabetics but likely applies to healthy individuals as well.
Reduced risk of cardiovascular disease – While this effect is not as notable as the reduction in the risk of colorectal cancer, the difference is still significant and applies to doses of 1000 IU or more.
Lowered risk of falling – The risk goes down significantly for older people who take the supplement. While this benefit may not seem too important (especially if you are young), falls become a huge problem for older people. This benefit appears to be enhanced by taking vitamin D along with calcium and vitamin K2.
Increased testosterone – While this effect is not too significant, it has been shown consistently in multiple studies that vitamin D supplementation does increase testosterone levels in men. It is important to note that no correlation between the supplement and free testosterone has been found. This effect only applies to total testosterone levels.
Fat loss – This effect may not apply to already lean individuals with a healthy body fat percentage. However, if you are obese or overweight, the supplement can help you lose fat.
Lowered symptoms of fibromyalgia – The degree of this effect is significant but it has been observed only in people who are deficient in vitamin D.
Improved asthma – Those who have higher levels of vitamin D in the blood experience fewer asthmatic attacks than those with lower levels.
Lowered blood pressure – While this effect is rather small and the evidence is somewhat conflicted, vitamin D does appear to lower blood pressure in those who are deficient.
Reduced rate of sickness – This effect is not as notable as the reduction in the severity of sickness. Nevertheless, the supplement reduces the risk for certain types of sickness, including respiratory tract infections (the reduction is over 50% in this case for people with a deficiency), pneumonia, influenza, and more.
Reduced symptoms of PMS (premenstrual syndrome) – Several studies show a reduction in the symptoms. While some have found only minor reductions, some show notable improvement.
Reduced symptoms of multiple sclerosis – Vitamin D has been shown to have some valuable immunomodulatory properties and reduce the formation of lesions.
Decreased symptoms of TCB (tuberculosis) – This effect is relatively minor.
Lowered triglycerides – The decrease in triglycerides is reliable but not too significant.
Reduced muscle cramps – Unfortunately, this effect was only noted in deficient girls who took 50000 IU per week. We need more studies to know whether it applies to other groups of people as well.
Decreased symptoms of Alzheimer’s disease – One study noted an improvement in IQ scores in people suffering from Alzheimer’s.
Height – While the supplement doesn’t seem to increase height in adults, it can support the growth of children. Those who had higher vitamin D levels in their childhood are overall slightly taller as adults. It is important to point out that no effect of vitamin D on growth hormone levels has ever been noted.
Unproven benefits
The effect of vitamin D on these parameters is either not sufficiently researched or the science shows little to no efficacy in these areas.
Cholesterol – If anything, vitamin D can slightly increase total cholesterol. Studies show either no effect or a slight increase in LDL cholesterol (up to 5%) due to the supplement. No change in HDL or VLDL-c has ever been noted. So there is not much to be concerned about but the supplement will not improve your cholesterol levels.
VO2 max – The supplement does not directly improve your VO2 max.
Total antioxidant capacity (TAC) – No notable effect has ever been noted.
Strength – Vitamin D supplements do not directly help you gain strength or muscle mass faster.
Sleep quality – The supplement does not appear to increase sleep quality. It also does not affect sleep duration.
Power output – Vitamin D does not influence power output during cardio or resistance training. It does not impact endurance either.
Fatigue – The supplement does not reduce symptoms of fatigue unless the fatigue is related to depression partially caused by vitamin D deficiency. In that case, the supplement could be of help.
Stress and anxiety – Unfortunately, no effect has ever been noted. Vitamin D supplements do not directly impact cortisol levels.
Weight loss – While the supplement can aid fat loss in obese and overweight individuals, it does not lead to overall weight loss.
Food intake – Vitamin D does not increase nor decrease your appetite for food.
Inflammation – No significant effect on CRP or other markers of inflammation has been observed.
Length of sickness – It is important to note that while vitamin D does reduce the intensity and rate of sickness, it does not seem to have any impact on how long the sickness will last. Some data shows a small decrease in the duration of upper respiratory tract infections but the evidence for this is limited.
Metabolic rate – The supplement does not speed up your metabolism.
Pain – Vitamin D doesn’t reduce the intensity of physical pain.
Possible side effects
These side effects are dose-dependent and the risk for them increases (most often linearly but sometimes exponentially) as you increase the dose. Some of the side effects are only relevant to very high doses.
Hypercalcemia – This is the main side effect associated with too much vitamin D. Excess calcium in the blood can weaken your bones, create kidney stones, and interfere with how your heart and brain function.
Kidney stones – A higher risk of kidney stones occurs when people take vitamin D together with calcium supplements.
Squamous dysplasia – This effect has been observed in one study but may not be causal.
Imbalance in fat-soluble vitamins – Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin K, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones. Fortunately, this is not as big of a problem when it comes to supplementing vitamin K as it is with vitamins A, D, or E.
Who should not take vitamin D?
You should probably avoid taking high doses of vitamin D if you:
already have high enough or too high vitamin D levels (40+ ng/mL)
have kidney stones
work outside or spend many hours a day outdoors
Who will benefit the most?
You should definitely consider taking vitamin D if you:
experience symptoms of vitamin D deficiency
have been tested for vitamin D blood levels and they are lower than would be optimal
have low levels of total cholesterol (it makes you absorb less of the vitamin)
are predisposed to colorectal cancer
suffer from fibromyalgia
experience depression during winter but not summer
live far from the equator
are under a lot of stress
take calcium (vitamin D helps calcium move from places like joints and arteries where it does more harm than good to places where it’s useful, such as bones)
have darker skin (since the darker your skin is, the less vitamin D you can absorb from the sun)
are older (older people also cannot absorb as much from the sun – on average, a 70-year-old person will absorb around 4 times less vitamin D from the sun than a 20-year-old)
are overweight (the more body fat you have, the more vitamin D is being stored in the fat cells and unable to enter the bloodstream)
use sunscreen (sunscreens block UVB radiation from sunlight, which means you don’t get as much vitamin D from sun exposure)
Signs of vitamin D deficiency
The main symptoms of deficiency include:
fatigue
bone pain
muscle weakness
muscle cramps
depression during winter
back pain
impaired wound healing
hair loss
nausea
constipation
poor appetite
increased thirst
increased urination
anxiety
Keep in mind that these signs are just indications of deficiency. The fact that you experience some of them does not necessarily mean that you need more vitamin D. On the other hand, some people may have a deficiency even though they are completely asymptomatic.
With that said, if you experience many or most of these symptoms, there is a high chance you are not getting enough of the vitamin. The more of these symptoms you experience and the more severe they are, the more likely you are deficient.
Forms of vitamin D
There are 2 main forms of Vitamin D. While they are extremely similar when it comes to their effects, there are some differences to consider.
Vitamin D2 (Ergocalciferol) – This form is mostly found in plants. The supplements are made from ergot mold. While it is not as bioavailable as the D3 form, the difference is not as big as some people believe. Some studies even show no difference at all, with the exception of megadosing (50000 IU or more taken at once), in which case D3 appears to be superior to D2.
Vitamin D3 (Cholecalciferol) – This is the main form found in the majority of supplements and is synthesized from 7-dehydrocholesterol. One benefit of D3 compared to D2 is higher shelf life. This means the supplement doesn’t lose potency as fast as the D2 form. Another reason to take D3 instead of D2 is that there is a lot more research on D3.
How much vitamin D should you take?
You want to take an amount that will help you reach the optimal level of vitamin D in the blood. This is the most important rule to follow.
Since too much vitamin D can be just as problematic as too little, we want to achieve a sweet spot that allows us to have enough vitamin D in the bloodstream but not too much.
The sweet spot is somewhere between 30-60 ng/mL (nanograms per milliliter). Even more specifically, 40-50 ng/mL appears to be the optimal blood concentration for most people.
Unfortunately, only around 70-80% of people in developed countries don’t have sufficient levels of vitamin D, which is why supplements are so important.
The RDA (recommended daily allowance) for vitamin D is 400-800 IU. This is, in most cases, too low. While this amount should be enough to prevent symptoms of severe deficiency, it is unlikely to help most people get to the optimal blood levels of vitamin D.
For an average person without a severe deficiency, 1000-3000 IU a day is usually the best amount to take.
However, how much you should take depends on many factors, such as your body weight, age, genes, how much sun exposure you get each day, etc.
Also, you should probably take more during winter than during summer since in the summer you are getting more of the vitamin from sun exposure.
The best way to truly know how much you should take is to routinely get tested for vitamin D concentrations in the blood. Again, you want the blood concentrations to be around 40-50 ng/mL.
While the upper tolerable intake level in the US is set to 4000 IU a day, many studies have shown that you can safely take more than that, so long as your blood levels are not too high already. Even doses of 10000 IU per day appear to be safe if you take them to fix a deficiency faster. This is not a bad idea at all since the sooner you can fix a deficiency, the better.
Food sources of vitamin D
Fish, seafood, and mushrooms are the only food sources that can provide a reasonable amount of vitamin D.
Both of these contain around 500 IU per 100 grams. Although in fish and seafood, the amount can vary greatly from type to type.
Mushrooms can produce vitamin D from UVB radiation (sun exposure), which makes them a great source of vitamin D2.
While some people believe that dairy and eggs are good sources of vitamin D, they do not contain a reasonable amount. Nor do other types of food.
The easiest way to find out how much vitamin D (and other nutrients) you are getting in your diet is with Cronometer.com – the app is free and allows you to track all vitamins, minerals, and more.
Best time to take vitamin D
Since vitamin D is fat-soluble, you need to take it with a source of fat if you wish to maximize its absorption.
As little as 10 grams of dietary fat should be enough. This amount may actually be better for increasing absorption than consuming more fat (30+ grams) but the difference is not significant.
Vitamin D from the sun does not require any dietary fat to be absorbed.
You may also want to take the supplement when you consume vitamin K and vitamin A since these fat-soluble vitamins increase the absorption of each other.
Whether you take vitamin D in the morning or the evening doesn’t really matter. Some people claim taking it in the morning is more natural and better for sleep but the supplement does not seem to impact your sleep or circadian rhythms in any way.
You also do not have to take vitamin D every day. There is not a big difference (if any) between taking 2000 IU every day and taking 14000 IU once a week.
Interactions with other supplements
Vitamin K The two vitamins share similar functions in the body and they act synergistically when it comes to improving bone and heart health. Vitamin K also appears to lower the risks associated with too much vitamin D. This is especially true for the K2 form but also applies to vitamin K1.
Vitamin A Vitamin A is protective against soft tissue calcification caused by excess vitamin D but it does not decrease the risk for hypercalcemia associated with the supplement.
Calcium Those with sufficient levels of vitamin D absorb calcium up to 2 times better. Vitamin D also helps calcium move from places like joints and arteries where it does more harm than good to places where it’s useful, such as bones. However, taking too much vitamin D with calcium could lead to hypercalcemia.
Magnesium Magnesium helps Vitamin D bind to its target proteins, as well as helping the liver and the kidneys to metabolize the vitamin.
Zinc Zinc helps the vitamin to work inside the cells.
Where to buy vitamin D
Amazon seems to be the best option for ordering vitamin D supplements in most countries. They offer some very affordable products that are backed by many positive reviews. Also, you can choose from a wide range of brands there without having to spend time searching through other markets on the Internet.
One thing you should pay attention to is that some brands display the dosage per serving and not per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
The supplement can be taken daily and does not need to be cycled.
Yes. Vitamin D doesn’t impact your sleep in any negative way.
The supplements rarely go bad but they can lose potency over time. The D2 form appears to lose potency faster than D3.
Keep your supplements in a cold, dark, and dry place and they will remain just as potent for many years.
Not much, unfortunately. The supplement does not improve your skin quality in a significant way. However, if you have dry skin related to vitamin D deficiency, supplements could be of help.
It doesn’t, unfortunately.
Yes, vitamin D can cause toxicity if taken at very high doses for a prolonged period of time. The main problem associated with the toxicity is hypercalcemia.
Fortunately, you cannot get too much vitamin D from the sun.
This depends mainly on how much you take. Higher doses will help you fix the deficiency faster. Even the most severe deficiency could be cured in a few weeks with very high doses. But be careful if you decide to do the megadosing strategy and get your blood tested on a regular basis to make sure you are not overdosing on the supplement and taking too much.
D3 is a form of vitamin D. However, you can almost use these terms interchangeably since most of the supplements contain the D3 form.
The main reason so many people are deficient is the lack of sun exposure. Humans used to spend way more time outside than we do in this day and age and our bodies have not yet accustomed to this way of living.
You probably need more vitamin D if you: – are under a lot of stress – experience symptoms of vitamin D deficiency – have been tested for vitamin D blood levels and they are lower than would be optimal – have low levels of total cholesterol (it makes you absorb less of the vitamin) – have darker skin (since the darker your skin is, the less vitamin D you can absorb from the sun) – – are older (older people also cannot absorb as much from the sun – on average, a 70-year-old will absorb around 4 times less vitamin D from the sun than a 20-year-old) – are overweight (the more body fat you have, the more vitamin D is being stored in the fat cells and unable to enter the bloodstream)
The D2 form is always vegan-friendly. As for the D3 form, it can either be derived from lichen of sheep’s wool.
References
Most of the information provided in this guide is based on scientific research that can be found and verified in the PubMed medical library. We excluded from consideration studies that are either confounded or have a high conflict of interest.
Anecdotal evidence (from reports on Reddit, YouTube, and other sources) is also taken into account unless it contradicts scientific research.
