This might surprise you, but Vitamin D is not really a vitamin.
It is, in fact, a hormone. A steroid hormone that your body produces when exposed to sunlight.
This is why you’ll often hear people calling vitamin D the sunshine vitamin.
However, sun exposure amongst people today is much lower than it was, say, 100 or 200 years ago. Our modern, fast-paced lifestyles have led us to spend most of our time closed away from the sun – becoming vitamin D-deficient.
In fact, over 40% of Americans are deficient in vitamin D, and many more don’t have optimal levels. Today, this number could be even higher. 
Vitamin D is absolutely crucial for optimal health. Without enough of this vitamin, our bodies can’t function optimally.
In fact, vitamin D deficiency leads to a whole host of health problems, including a poor immune system, weak bones, cardiovascular diseases, and seriously low testosterone. 
In this article, I’ll cover the risks and dangers associated with low vitamin D levels. I’ll also go in-depth about its benefits, dosage, safety profile, and more – using science as my guide.
What is Vitamin D
Vitamin D is a fat-soluble nutrient. This means that it dissolves in fat. This is why when you take a vitamin D supplement, you need to take it with a meal or a fat source – otherwise, it cannot be absorbed in your body.
D vitamin can also be accumulated and stored in your body fat tissue for long periods of time.
Other fat-soluble vitamins include vitamin A, E, and K.
You might have heard of vitamin D3 before, but there are actually 5 types of this nutrient. Including D1, D2, D3, D4, and D5.
The two most common ones are vitamin D2 and D3 – you’ll find these in your diet. Foods such as fatty fish, egg yolks, and certain types of mushrooms contain it. 
Of all these types, vitamin D3 is the one that’s the most effective and brings the biggest health benefits. That’s why when talking about the benefits and effects of D vitamin in general, I’m actually talking about vitamin D3. [6, 7]
To sum it up:
Vitamin D is a fat-soluble nutrient, meaning it gets dissolved in fat and can be stored in the body for long periods of time. There are 5 types of vitamin D, but we can only get D2 and D3 through our diet. D3 is the most potent form of vitamin D and offers biggest health benefits.
How Vitamin D Works
The Process of Conversion
In order to become “active”, Vitamin D has to go through a number of processes in the body. Specifically, it has to pass two conversion steps – after which it becomes active and usable by your system. [8, 9]
First off, it gets converted to 25(OH)D, AKA, calcidiol in your liver. This is the type of vitamin D which your liver stores for further use.
Then, if your body actually needs to utilize vitamin D, it converts it to calcitriol, or 1,25(OH)2D if you like fancy names. This second step of the process takes place in the kidneys.
After this two-step conversion, it becomes the active, steroid hormone vitamin D as we know it.
What it Does in Your Body
When it binds to the receptors, it either turns certain genes on or off, depending on what your body requires at that particular moment. This ultimately leads to changes in your very cells. This is how most natural steroid hormones work. [12, 13]
Since it affects countless cells in the body, vitamin D plays a role in numerous bodily processes.
For example, it affects the bone health by signaling the cells in your gut to start absorbing phosphorus and calcium.
If you’re deficient in vitamin D, it means you’re also deficient in calcitriol, which is the steroid hormone form of vitamin D.
The implications this has on one’s health can become serious over time. Keep reading to find out what they are.
To sum it up:
Vitamin D is first converted into calcidiol, which your body stores for further use. Then, it gets converted by your body into calcitridol – the active steroid hormone vitamin D. It then binds to receptors in your body, regulating countless processes – from the immune system, hormone production, to metabolism.
Types of Vitamin D
There are a total of 5 vitamin D forms that exist.
However, only 2 of these are used by our body and found in foods – they are vitamins D2 and D3. These two belong in the calciferol group.
Other types of D vitamin include D1, D4, and D5. All of which I’ll explain in further detail below:
Vitamin D1 is a mixture of ergocalciferol (vitamin D2) and lumisterol, in the 1:1 ratio.
Lumisterol is a steroid compound which belongs in the vitamin D family. It’s produced as a photochemical by-product in the process of creation of vitamin D1. 
Also known as ergocalciferol, vitamin D2 is one of the major types of vitamin D, alongside D3.
It’s found in foods and sometimes used in dietary supplements. However, it’s far inferior to vitamin D3, which has better bioavailability and effectiveness in the body.
As a supplement, vitamin D2 helps treat and prevent deficiency in vitamin D. It also offers all of the other benefits that standard vitamin D supplementation offers, although to a much lesser degree than the D3 form of the vitamin. 
Also called cholecalciferol, this is the most bioactive form of vitamin D. Your skin creates it when under direct exposure to UVB sun rays.
Other vitamin D3 sources include supplements, as well as foods such as egg yolks, fatty fish, and liver.
For this reason, you’ll mostly find D3 in high-quality supplements. It’s far more effective in not just raising vitamin D blood levels, but also treating deficiency, improving the immune system, and boosting steroid hormones such as testosterone (I’ll cover this in more detail in second). 
The fancy name for this vitamin is 22-Dihydroergocalciferol.
While it isn’t used or produced by your body for anything really, it can be found in certain species of mushrooms.
Vitamin D5 is another form of D vitamin. It’s made from 7-Dehydrositosterol, which is a sterol and the direct precursor of vitamin D5.
Effects of Low Vitamin D
Low vitamin D is a dangerous business.
Despite this, deficiency in this vitamin is one of the most common deficiencies out there.
Naturally, there are certain groups of people which have a greater risk of low vitamin D levels than others. The average deficiency in America is around 40%, but this percentage shoots way up in black people and Hispanics – between 69-82%! 
Elderly people, and those who suffer from certain types of illnesses are also likely sufferers of vitamin D deficiency. In fact, research has shown that 96% of heart attack victims had low vitamin D levels. [24, 25]
Some people aren’t deficient, but that doesn’t mean they have optimal levels of D3 either. Studies suggest that most people actually don’t have optimal levels of D3, which are around 30 ng/mL.
Vitamin D deficiency isn’t easy to detect. The symptoms usually creep up slowly, over the years and decades. That’s why vitamin D deficiency is called a silent epidemic among people worldwide.
Signs of Deficiency
Even though it’s often hard to detect, there are some common signs that are linked to low vitamin D levels. The most severe ones include rickets (a bone disease), osteoporosis, autoimmune diseases, diabetes, cancer, dementia, and cardiovascular issues. 
Deficiency in D3 is also linked to low testosterone.
Other symptoms of vitamin D deficiency include:
- Chronic fatigue
- Poor athletic performance
- Feeling sleepy all the time
- Insomnia (ironically)
- Belly fat and “love handles”
- Mood Swings
- Depression and Anxiety
- Weak and Easily Broken Bones
- Chronic inflammation
- Getting sick constantly (weak immune system)
That said, the science still isn’t clear on whether low vitamin D levels contribute to these health issues, or whether people with vitamin D deficiency are at a higher risk of getting them.
To sum it up:
Vitamin D deficiency is extremely common. On average, 41% Americans, 69% Hispanic people, and 82% black people suffer from it. Low levels of this vitamin lead to a number of health issues, including heart disease, diabetes, osteoporosis, low testosterone, weak immune system, and increased risk of death – just to name a few.
Best Sources of Vitamin D
The best source of vitamin D is the sun.
When your skin gets exposed to direct UVB sun rays, it uses cholesterol to start producing vitamin D. 
If you live in a sunny area, chances are you can get enough vitamin D by spending 20-30 minutes outside every day. If you live in a place where there’s not a lot of sun, however, then consider taking a D3 supplement.
When going under the sun, make sure to expose most of your body. If you only expose your hands and face, your body will naturally produce much less vitamin D3.
Glass and sunscreens also block vitamin D production. This is because UVB rays can’t penetrate through them.
For this reason, the advice to never go under the sun without a sunscreen is questionable. In fact, by putting the sunscreen on, you’ll be at a higher risk of vitamin D3 deficiency, leading to many other diseases – including cancer. 
However, this doesn’t mean you should jump outside and spend the next 6 hours under the sun. That will only make things worse. Whenever you spend time in the sun, make sure not to burn yourself.
So what should you do?
I suggest going under the sun without any sunscreen for about half an hour. After that, apply it to prevent sunburn.
Obviously, the amount of time you should spend under the sun without the sunscreen depends on your sensitivity.
If you rarely go under the sun, then even 20 minutes of direct exposure on a hot summer day can cause a sunburn. Be smart, and slowly adapt yourself to sun rays.
Foods are unfortunately one of the worse ways of getting vitamin D. This is because very few foods naturally contain it.
Here’s the table of foods that are naturally rich in this vitamin. As you’ll see, only a handful of them contain decent doses.
|Type of Food||Amount of Vit-D||% Daily Value|
|Cod liver oil (1 tablespoon)||1,360 IU / 34 mcg||227%|
|Cooked salmon, 3 oz (85 grams)||447 IU / 11 mcg||75%|
|Canned tuna, 3 oz (85 grams)||154 IU / 4 mcg||26%|
|Cooked beef liver, 3 oz (85 grams)||42 IU / 1 mcg||7%|
|1 large egg (yolk is where D is contained)||41 IU / 1 mcg||7%|
|Canned sardines, drained||23 IU / 0.6 mcg||4%|
While fish like salmon and tuna do have a decent amount of D3, you’d need to eat them practically every day to get the long-term, optimal benefits.
The only good food source of the D vitamin is cod liver oil. A single tablespoon will give you enough of D3 for two days. However, there’s a risk of heavy metal poisoning with seafood. Such as mercury and lead.
Foods such as dairy and cereals are fortified with D3, but they contain fairly low doses of the vitamin. You’d have to eat plenty of dairy and cereal every day to obtain enough of this vitamin, but these foods aren’t healthy for you in high amounts – which is a topic for another article. 
If you can’t spend at least 20 minutes under the direct sunlight every day, then supplementing with Vitamin D will be your best bet.
- Improved cardiovascular health
- Enhanced cognition (better memory recall and other cognitive functions)
- Better athletic performance (more strength, stamina)
- Increased testosterone levels
- Stronger immune system
Supplementing With Vitamin D
Currently, RDA for vitamin D is between 400-800 IU per day in most countries. However, studies are beginning to show that this is far too low for adults. 
In USA and Canada, the safe upper limit for D vitamin is 4,000IU daily.
However, modern research shows that the actual upper limit is 10,000IU daily. This is the dosage doctors often recommend to their patients in a case of severe deficiency, where their vitamin D blood levels fall below 12 ng/mL. 
So how much vitamin D should you take?
Well, that depends on what you’re shooting for.
For example, a dose for general health is not the same as dosage for boosting testosterone.
Here I’ll cover the best dosages for different goals, such as fat loss and athletic performance.
Take a look:
Dosage For Overall Health
For general health purposes, take between 1,000-2,000IU of D3 daily. This is the lowest effective dosage range and is enough to meet the needs of most people.
However, for specific purposes such as boosting energy and testosterone, you’ll need a higher dosage.
Dosage For Energy
For an increased energy, studies suggest that the optimal dosage for D3 is 5,000IU daily.
One study, in particular, caught my attention. Researchers tested two groups of people who were deficient in D vitamin. One group took 2,000 IU of D3 daily, while the other took 5,000 IU each day.
Dosage For Increased Testosterone
Studies that tested the effects of D3 on testosterone discovered that the optimal dosage is somewhere between 3,000-4,000IU daily.
Dosage For Metabolism
To improve fat loss, take between 1,000-2,000IU of vitamin D every day.
In one study, a group of overweight and obese volunteers took 1,000IU of D3 daily. After 12 weeks, their body fat percentage reduced significantly. 
Dosage For Athletic Performance
To improve your speed, strength, energy, and testosterone, a dosage between 3,000-5,000IU daily is ideal.
Obviously, if you don’t expose yourself to any sunlight at all, a higher dosage is better – such as 5,000IU. 
Can You Overdose on Vitamin D?
Although possible, it’s extremely rare for someone to overdose on vitamin D.
To reach toxic doses, you’d need to take over 50,000IU or 1,250 micrograms every single day for several months or longer. 
Can you overdose on vitamin D3 from the sun? No, you can’t. 
Still, dosages higher than 5,000IU don’t appear to offer any additional benefits. So unless your doctors tell you so, there’s no need to take more than 5,000IU of D3 daily.
A dosage of around 3,000IU will be enough for pretty much everyone. Both those who want general health benefits, and men who want to boost their testosterone.
Vitamin D is a fat-soluble nutrient that your skin synthesizes when exposed to the direct sunlight.
There are 5 types of vitamin D: D1, D2, D3, D4, and D5. However, only two of those are actually utilized by your body – D2 and D3. D3 is the most potent form of D vitamin. It provides the strongest effects and biggest health benefits.
Getting enough vitamin D is essential for your health. It improves your bone density, metabolism, strength, testosterone, overall health, and reduces the risk of cancer and death.
Still, many people seem to disregard its importance. Over 40% Americans are deficient in D3. That number goes even higher in Hispanic and black people – up to 82%!
A deficiency in D vitamin leads to heart disease, rickets, osteoporosis, cognitive issues, low testosterone, and an increased risk of death from all causes.
The current recommended dosage for D3 is between 400-800IU daily. However, modern research suggests this is too low for adults.
For general health benefits, it’s safe to take between 1,000-2,000IU daily. If you’re looking to improve energy, testosterone, and athletic performance while burning fat, then higher dosages will be more effective. Such as 5,000IU of D3 daily.
The best source of vitamin D is the sun. However, if for whatever reason you can’t get at least 20-30 minutes of strong sunlight daily, then consider taking a D3 supplement. It’s a safe and effective way of reaping all of the benefits this vitamin has to offer.