The Science of Vitamin D 

15 min read

key takeaways:
  • Vitamin D is a super important nutrient for your health and well-being.
  • Vitamin D deficiency can cause problems like fatigue, bone pain, hair loss, and more infections.
  • Find out the best sources of vitamin D and exactly how much you need in a day.

We're breaking down vitamin D in it's entirety to help you understand how much you really need, how to choose the best sources, and the key to optimal health.

Vitamin D — often called the "sunshine vitamin" — plays a crucial role in maintaining good health. Produced naturally by the body when exposed to sunlight, vitamin D is essential for maintaining strong bones, a healthy immune system, and may even help reduce the risk of certain diseases like multiple sclerosis and diabetes.

According to health experts, adequate levels of vitamin D are important for people of all ages, and understanding how to properly obtain and maintain those levels is key to overall well-being.

In this guide, we will delve into the importance of vitamin D, how to ensure optimal levels, and potential benefits for the human body. Plus we will explore the two forms, their sources, and discuss the recommended daily intake appropriate for different age groups and lifestyles.

So, What Exactly Is Vitamin D?

Vitamin D is a fat-soluble nutrient along with vitamins A, E, and K. And it’s one of the 24 micronutrients critical for human survival. The sun is the best way of naturally getting enough vitamin D through our skin. But vitamin D is also found naturally in fatty fish (such as salmon, tuna, mackerel) and eggs. It can also be found in plant-based foods like mushrooms and fortified foods, although the type of Vitamin D can vary (Vitamin D2 vs. D3) but more on that in a bit.

Compared to other nutrients, vitamin D functions more like a hormone in the body than a micronutrient. There is also research showing that vitamin D plays a part in the different endocrine pathways, meaning that a vitamin D deficiency can be considered as a hormonal deficiency.1

Forms of Vitamin D

There are two main forms of vitamin D: D2 (ergocalciferol) and… D3 (cholecalciferol)Vitamin D2 is found in some plant-based foods, while vitamin D3 is produced in the skin when exposed to sunlight and is also found in animal-based foods like fatty fish, egg yolks, and liver.

How does vitamin D work?

Vitamin D binds to and activates vitamin D receptors (VDR) in our cells. Activating these receptors can lead to a change in the genetic expression of dozens — if not hundreds — of genes.

Dangers of Vitamin D Deficiency

There are a lot of life altering dangers you can get from vitamin D deficiencies, for example:

1. 55x more likely to have bone fracture requiring surgery2

AIS is an injury severity rating scale which assigns a number to an injury description on a scale of 1 (minor) to 6 (fatal). So, crushed pelvis would be an AIS 4 and a small hairline fracture would be an AIS 1. The higher the AIS, the more likely it is that you’ll need surgery. This study showed that kids with lower vitamin D levels were found to be at higher risk for more severe fractures. So, if you have low vitamin D, you’re 55 times more likely to get a worse injury and end up needing surgery.

2. 30x more likely for lung disease becoming suddenly worse3

Chronic obstructive pulmonary disease (COPD) is a common lung disease causing restricted airflow and breathing problems. It is sometimes called emphysema or chronic bronchitis. COPD is the third leading cause of death worldwide, causing 3.23 million deaths in 2019. This study showed that if you have severe vitamin D deficiency, then it’s 30 times more likely for your lung disease to get worse and get hospitalization.

3. 25x more likely to have cognitive problems4

Mild cognitive impairment (MCI) is an early stage of memory loss or other cognitive ability loss (such as language or visual/spatial perception) in people who maintain the ability to perform most daily activities. This study showed that you’re 25 times more likely to have cognitive problems, if you have a vitamin D deficiency.

4. 23x more likely to have vertigo5

Benign paroxysmal positional vertigo (BPPV) is one of the most common causes of vertigo — the sudden sensation that you're spinning or that the inside of your head is spinning. This study showed an association between idiopathic BPPV (vertigo) and decreased serum vitamin D. Decreased vitamin D may be a risk factor of vertigo.

5. 19x more likely to get dementia6

Dementia is the decline of mental function that’s severe enough to interfere with daily living. The study found that you’re 19 times more likely to get dementia if you have a vitamin D deficiency.

Other Stats Regarding Vitamin D Deficiency

17x more likely to have muscle inflammation

14x more likely for dark-skinned children to get Type 1 diabetes

12x more likely to die from elderly pneumonia

11x more likely to be allergic to peanuts

9x more likely to have gastric cancer

8x more likely to have autoimmune hepatitis

8x more likely for alcoholic to have alcoholic liver disease

8x more likely to get lupus

7x more likely to have low birth weight infant

7x more likely to have leg pain

7x increased chance of death from coronary artery disease

6x more likely to get hip fracture after stroke

6x more likely to die after coronary bypass

6x more likely to have allergic rhinitis

6x worse outcome after sudden cardiac arrest

6.5x more likely for infant to be small for gestational age

6x more likely to get cancer in children


Common Causes of Vitamin D Deficiency

Vitamin D deficiency is a common issue that affects people of all ages and backgrounds. There are several factors that can lead to a deficiency in this essential nutrient, including:

Not Spending Enough Time Outside

It’s pretty evident that most people don’t spend enough time outside in the sun. And there are a few reasons for this.

One reason is that people now have more indoor office jobs, instead of outdoors jobs (like construction). If you’re spending 8 hours of the day indoors, then when can you get some sun?

Another reason is that people spend more time on their phones and computers. As the amount of time that people spend inside on their devices playing video games, watching YouTube and scrolling through social media means less time is spent outdoors getting natural sunlight.

We also use more windows now. How are windows relevant? Well windows block UVB light — which produces vitamin D — and lets in UVA light — which can damage the skin. So if the little bit of sunlight that you are getting is through a window, you’re actually making things worse.

Lastly, most of us are living in cities, where we don’t have many parks or outdoor activities, and the air pollution can make it harder for UVB light to pass through and reach our skin.

Vitamin D Deficiency in Modern Diets

Newsflash! There is a huge problem with the Standard American Diet. But it’s not just westerners that have undergone massive transformations from what our ancestors used to eat.

Changes in dietary patterns that have deviated away from ancestral diets have accelerated exponentially over the past few decades.

The one thing that kicked it into high gear is the confusion about cholesterol. Ever since we were fed the diet heart hypothesis — that cholesterol from the fat we eat causes heart attacks — we’ve been eating less fat and getting less cholesterol in our diet.

Here’s the kicker: we need cholesterol to make vitamin D.

“Our most important hormones depend upon adequate reserves of cholesterol for their production and nowhere is this more important than as the precursor substance for the synthesis of Vitamin D, known also as calcitriol.

Researchers [...] pronounce that we are in the midst of an epidemic of vitamin D deficiency of immense proportion.”

— Duane Graveline MD, former NASA Astronaut, former USAF flight surgeon, and retired family doctor

In fact, Dr Weston Price noticed that native tribes got ten times the fat-soluble vitamins and one-and-a-half to fifty times more minerals than people in the United States.

Today, we’re drinking more skim milk or plant-based milk instead of raw whole milk,7 eating less fatty meat, and using more seed oils (polyunsaturated fats) instead of butter, lard, and tallow (saturated fat). These significant changes in dietary food choices and preferences combined with sedentary lifestyles lived indoors under artificial lighting compounds to create a severe deficiency of vitamin D in modern lifestyles!

To make matters worse:

Meat from factory farms has far less vitamin D than from free-range farms. We eat little to no liver which is a powerhouse of vitamin D. And we don’t get enough magnesium because our soils are depleted. Magnesium is a cofactor for vitamin D, which means not enough magnesium makes your body unable to use the vitamin D.

The Link Between Vitamin D and Obesity

Obesity and vitamin D deficiency are linked together for a few reasons.

  • Obese people need more vitamin D because as a fat-soluble vitamin it gets trapped (and stored) in fatty tissues instead of circulating in the bloodstream where it can get to work.
  • On average, obese people spend even less time in the sun (this is a problem all of us face, but it’s worse for obese people).
  • Their livers don’t function properly due to a disease called Non-Alcoholic Fatty Liver Disease so they don't process vitamin D efficiently.

In fact, there’s even research showing that a lack of vitamin D in the womb can lead to higher risk of obesity later in life.8 There’s also research showing that getting extra vitamin D can help those struggling with obesity actually lose weight faster.9 10

The Problem with Sugar & Vitamin D Absorption

There are a lot of rodent studies showing that fructose reduces vitamin D levels. A study from 2014 showed that rats on a high fructose diet had less vitamin D in their blood. Another study, this time in 2013, showed that rats on fructose had poor intestinal function. Their ability to absorb calcium and vitamin D had reduced because of fructose.11

So, you might wanna cut down on the sodas and the desserts to absorb vitamin D better.

Symptoms of Vitamin D Deficiency

Here are some common symptoms of vitamin D deficiency:

   •  Fatigue and tiredness
   •  Bone pain and muscle weakness
   •  Depression and mood changes
   •  Impaired wound healing
   •  Hair loss
   •  Increased risk of infections

It's important to note that these symptoms can be caused by a variety of factors and may not necessarily indicate a vitamin D deficiency. However, if you're experiencing any of these symptoms, it's a good idea to speak with your healthcare provider to determine the underlying cause.

Additionally, some people may be more at risk for vitamin D deficiency than others. These include:

GroupReason for Increased Risk
Older adultsReduced ability to synthesize vitamin D from sunlight
People with dark skinHigher levels of melanin reduce the skin's ability to produce vitamin D
People with limited sun exposureThose who spend most of their time indoors or cover their skin with clothing or sunscreen may not get enough vitamin D from sunlight
People with certain medical conditionsConditions such as Crohn's disease, celiac disease, and cystic fibrosis can interfere with the body's ability to absorb vitamin D

If you suspect that you may be deficient in vitamin D, talk to your healthcare provider. They can perform a blood test to measure your vitamin D levels and recommend appropriate treatment if necessary.

How To Test For Vitamin D Deficiency

The easiest way to test your vitamin D levels is through a blood test that measures circulating vitamin D. This test is known as 25-OH-vitamin-D. While the levels of 25-OH-vitamin-D that indicate a deficiency are clearly defined, it is unclear when we consider what is optimal.

As a fat-soluble vitamin, vitamin D gets stored in fat tissue and cells. Vitamin D is absorbed into fat and muscle cells and stored for later use. When these cells reach capacity, vitamin D is released back into the bloodstream over time, contributing to vitamin D distribution. The better the body stores are satisfied, the higher circulating vitamin D levels will be, which provides the assessment of vitamin D levels in blood work.

Although 25-OHD isn't the active form of vitamin D our body uses, it is a good indication of supply. The vitamin D hormone calcitriol is the usable form of vitamin D. The body converts vitamin D to calcitriol as needed. This can be highly variable, so 25-OHD provides a better measurement for vitamin D. Another important factor to pay attention to with testing is the units used.

Currently, two different units of measurement are used: ng/ml and nmol/l. This frequently leads to confusion because a reading of "90" could indicate very different results.

For a more complete guide about optimal Vitamin D intake and references as well as other hard-to-get essential nutrient targets, check out our Essential Nutrition Guide.

Health Benefits of Vitamin D

Vitamin D has a ton of health benefits ranging from improving bone health to supporting a robust immune system. Here are some of them:

   •  Vitamin D improves the immune system.12
   •  It protects our body from seasonal illnesses like colds, coughs, and flu.13
   •  Vitamin D reduces the risk of Alzheimer's disease and other cognitive-related impairments.14
   •  Vitamin D has anti-inflammatory properties known to keep our lungs healthy.15
   •  Vitamin D is a perfect partner to calcium, making it beneficial to our bones, muscles, and balance.16
   •  Vitamin D has been shown to help with depression.17
   •  Vitamin D might have a role in cancer prevention and treatment.18
   •  Vitamin D may even reduce the risk of getting type 2 diabetes.19

Vitamin D might appear to be a simple nutrient. However, Vitamin D deficiency causes serious health problems. And to treat it properly, we need to enlighten ourselves with the factors that cause it.

New Study on Vitamin D and Brain Health

A new research paper suggests that vitamin D in the brain could help people function better as they age. The study found that vitamin D can protect against cognitive decline and improve memory and learning abilities.

The researchers believe that vitamin D may help to protect the brain from damage caused by inflammation and oxidative stress. The study highlights the importance of maintaining healthy levels of vitamin D throughout life, particularly as people age.21

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Food Sources of Vitamin D

Vitamin D is an essential nutrient that can be obtained through food sources or exposure to sunlight. While sunlight is the most natural way to get vitamin D, certain foods can also be a great source of this nutrient.

Foods that are high in vitamin D include:

   •  Fatty fish such as salmon, tuna, and mackerel
   •  Egg yolks
   •  Cheese
   •  Mushrooms
   •  Fortified foods such as milk, orange juice, and cereal

It's important to note that while some foods may contain vitamin D, the amount may not be sufficient for daily intake. Additionally, some people may have difficulty absorbing vitamin D from food sources alone.

If you're concerned about your vitamin D levels, it may be helpful to speak with a healthcare professional about supplementation or other ways to increase your intake.

Supplements for Vitamin D Deficiency

While it is always best to get your daily dose of Vitamin D from natural sources, such as sunlight and food, sometimes it can be difficult to get enough. This is especially true for people who live in areas with little sunlight or who have a restricted diet. In these cases, supplements can be a great way to ensure that you are getting enough Vitamin D.

There are two main types of Vitamin D supplements: Vitamin D2 and Vitamin D3. Vitamin D3 is the preferred form, as it is more easily absorbed by the body. It is important to speak with your doctor before taking any supplements, as they can interact with other medications and may not be safe for everyone.

It is also important to note that taking too much Vitamin D can be harmful. The recommended daily amount for adults is 600-800 IU per day but functional medicine guidelines use a much higher target of up to 5,000 IU per day. However, it is not recommended to take more than 4,000 IU per day without first consulting a healthcare provider.

If you are deficient in Vitamin D, your doctor may recommend a higher dosage of supplements to bring your levels back up to normal. This is typically done through a short-term (6-week) course of high-dose Vitamin D supplements (50,000 IU per week), followed by a maintenance dose to keep levels stable.

How Much Vitamin D Do I Need?

The recommended daily intake of vitamin D varies depending on age, sex, and other factors.

But here’s a general guideline:

Everyone older than 11 years should be taking at least 2000 IU of vitamin D daily everywhere around the world.

I know that the 2010 US standard specifies a minimum of 400 or 600 IU. But, that‘s like earning minimum wage — really hard to live on.

Why you should take Vitamin D with Vitamin K2

Due to the complex nature of vitamin D, just increasing your vitamin D intake may not be enough. Other issues that could be limiting your ability to synthesize and use vitamin D may exist. Magnesium and vitamin K2 both play a critical role in our body's ability to convert and use vitamin D. It just so happens that both these nutrients are also in short supply in modern lifestyles.

Like most minerals or nutrients, when you're unable to get yourself to a level that is healthy, that's where supplements can prove to be beneficial! Depending on your vitamin D levels, you may need anywhere between 2,000 and 5,000 IU of vitamin D daily to attain and maintain an optimal supply. When considering a vitamin D supplement be sure to look for natural forms of vitamin D and the inclusion of vitamin K2 as all-trans MK-7.

Vitamin K2 is most common in fermented foods and grass-fed animal products. This makes K2 challenging to get through the diet. The standard American diet doesn't usually include these choices, and vegan diets restrict meat consumption, which makes it almost impossible to get everything you need from food alone.

And, even if you happen to fall into the small percentage of people who actually eat these foods on a regular basis, you can still experience a Vitamin D deficiency or insufficiency due to a Vitamin D malabsorption or simply due to the fact that the amount of vitamins and minerals in almost all our food is in decline due to a loss of biodiversity and nutrients in our soil.

Now, if you're looking for a product that satisfies your vitamin D + K2 criteria that is both soy-free and vegan-friendly and is more enjoyable to take than a handful of pills and capsules, check out our Essentials Nutrition Shake. We formulated it to provide 1200 IU of vegan vitamin D3 with optimal levels of K2 from fermented chickpeas. Additionally, you'll get a bump in magnesium to complete the trio of essential vitamins and minerals needed for optimal vitamin D intake and usage.

Side Effects and Overdose

While Vitamin D is essential for our health, too much of it can actually be harmful. In this section, we'll explore the side effects and potential overdose implications of excessive Vitamin D intake.

Side Effects

Common side effects of taking too much Vitamin D are usually mild and temporary. These may include:HeadachesNausea and vomitingLoss of appetiteMood swings - imagine turning into a grouchy squirrel!Constipation or diarrheaMost of these side effects can be avoided by sticking to the recommended daily intake of Vitamin D.

Here's how to combine them

The most popular way to combine vegan proteins is by blending pea protein with brown rice.

PROS: The brown rice has complementary SAAs that the pea is missing, while the pea has plenty of lysine to cover for the brown rice. Brown rice is also a highly cost-effective protein, which means most pea + rice mixes are relatively affordable.

CONS: Brown rice often yields a ‘chalky’ taste and texture, and you don’t get as broad a range of micronutrients. This challenge, however, can easily be overcome by first sprouting the grains to make them more bioavailable and cleaner tasting.

And this exactly what we've done in our Essentials Shake.


In conclusion, there are a lot of dangers of not getting enough vitamin D — like risk of fractures, cognitive decline, dementia, and even obesity. And there are a lot of reasons why you might be deficient.

So, understanding what risk factors you have, knowing how much vitamin D you’re getting and the way various nutrients interact with vitamin D is crucial for optimizing its benefits and maintaining overall health. You need to aim for a balanced diet that includes a variety of vitamins and minerals to ensure your body gets the support it needs.

And if you want or need a quick and easy way of getting high quality micronutrients including vitamin D, then you should check out our Essentials Nutrition Shake. The Essentials Shake is the only shake designed to fill the most common nutritional gaps of modern diets and one of the only complete nutrition shakes on the market that provides an optimal maintenance dose of Vitamin D3 + K2…giving you more of what you need and less of what you don’t.


1. Bodnar et al. “High prevalence of vitamin D insufficiency in black and white pregnant women residing in the northern United States and their neonates.” The Journal of Nutrition vol. 137, 2 (2007): 447-52. <>

2. Minkowitz et al. “Low Vitamin D Levels are Associated With Need for Surgical Correction of Pediatric Fractures.” Journal of pediatric orthopedics vol. 37,1 (2017): 23-29 <>

3. Malinovschi et al. “Severe vitamin D deficiency is associated with frequent exacerbations and hospitalization in COPD patients.” Respiratory Research vol. 15,1 131 (2014) <>

4. Annweiler et al. “Vitamin D insufficiency and mild cognitive impairment: cross-sectional association.” European journal of neurology vol. 19,7 (2012): 1023-9 <>

5. Jeong et al. “Decreased serum vitamin D in idiopathic benign paroxysmal positional vertigo.” Journal of Neurology vol. 260, 3 (2013): 832-8. <>

6. Annweiler et al. “Serum vitamin D deficiency as a predictor of incident non-Alzheimer dementias: a 7-year longitudinal study.” Dementia and geriatric cognitive disorders vol. 32,4 (2011): 273-8. <>

7. Vanderhout et al “Higher milk fat content is associated with higher 25-hydroxyvitamin D concentration in early childhood.” Applied physiology, nutrition, and metabolism vol. 41,5 (2016) <>

8. Lundy et al “Vitamin D Deficiency During Development Permanently Alters Liver Cell Composition and Function.” Frontiers in Endocrinology vol. 13 (2022) <>

9. Mason et al “Vitamin D3 supplementation during weight loss: a double-blind randomized controlled trial.” The American journal of clinical nutrition vol. 99,5 (2014): 1015-25 <>

10. Hanafy et al “Beneficial Effects of Vitamin D on Insulin Sensitivity, Blood Pressure, Abdominal Subcutaneous Fat Thickness, and Weight Loss in Refractory Obesity.” Clinical Diabetes (American Diabetes Association) vol. 36,3 (2018) <>

11. Douard et al “Excessive fructose intake causes 1,25-(OH)(2)D(3)-dependent inhibition of intestinal and renal calcium transport in growing rats.” American Journal of Physiology. Endocrinology and Metabolism vol. 304,12 (2013) <>

12. Cantorna et al, “Vitamin D status, 1,25-dihydroxyvitamin D3, and the immune system” The American Journal of Clinical Nutrition, Volume 80, Issue 6 (2004) <>

13. Hughes and Norton, “Vitamin D and respiratory health.” Clinical and experimental immunology vol. 158,1 (2009): 20-5. <>

14. Annweiler at al, “Higher Vitamin D Dietary Intake Is Associated With Lower Risk of Alzheimer’s Disease: A 7-Year Follow-up” The Journals of Gerontology: Series A, Vol. 67, 11 <>

15. Hansdottir and Monick, “Vitamin D Effects On Lung Immunity And Respiratory Diseases” Vitamins and hormones vol. 86 (2011): 217-37. <>

16. Turner et al “Vitamin D and bone health” Scandinavian Journal of Clinical and Laboratory Investigation, 72:sup243,65-72, <>

17. Menon et al, “Vitamin D and Depression: A Critical Appraisal of the Evidence and Future Directions” Indian J Psychol Med (2020) <>

18. Vuolo et al, “Vitamin D and cancer” Front. Endocrinol. Vol 3 (2012) <>

19. Mathieu et al, “Vitamin D and diabetes” Diabetologia 48, 1247–1257 (2005) <>

20. Shea et al. “Brain vitamin D forms, cognitive decline, and neuropathology in community-dwelling older adults.” Alzheimer's & Dementia: The Journal of the Alzheimer's Association, 10.1002/alz.12836. (2022) <>

Disclaimer: The LYFE Fuel blog is for informational purposes only. The information does not serve as a replacement for professional medical advice or treatment. We kindly ask you not to ignore professional medical advice because of any information you’ve read on If you have any concerns about your health, please consult a physician or appropriate health care expert.