VITAMIN D: Benefits, Dosage, Deficiency, Warnings and Precautions

Jessica Lewis
March 14, 2017
Vitamin D is essential for a vast palette of processes in our bodies. It maintains bone and teeth health, it stimulates all sorts of brain functions, optimizing our mental health, it strengthens our immune system, and it also balances our weight and appetite. So far, research has shown that low levels of vitamin D are linked to various cancer types and other severe diseases.

We’ve gathered and analyzed all the essential information you need to know about vitamin D and its beneficial effects on the overall health of the body.

What is Vitamin D and How Does It Work?

Vitamin D involves a class of fat-soluble secosteroids that stimulate the intestinal absorption of iron, calcium, magnesium, phosphate and also zinc. In human beings, the essential compounds within this group are vitamin D3 or cholecalciferol and vitamin D2 or ergocalciferol. These two forms of vitamin D can be consumed from diet and through supplementation. Unfortunately, there are very few foods in which vitamin D can be found. On the other hand, the major natural source of vitamin D is its synthesis in our skin. Dermal synthesis of vitamin D depends on our exposure to the sun, especially to UVB radiation.

Vitamin D provided by food and by dermal synthesis due to sunlight is biologically inactive; the vitamin’s activation requires an enzymatic conversion that happens in the kidneys and also in the liver.

According to research and scientific studies, the synthesis of vitamin D due to exposure to the sun is usually regulated by something that scientists call a negative feedback loop with the goal of preventing toxicity. Specialists don’t offer any specific recommendations regarding the amount of time we require spending in the sunlight to reach optimal vitamin D requirements. The main reason for their lack of advice is the risk of cancer associated with radiations that come from the sun.

Most mammals exposed to sunlight can synthesize proper amounts of vitamin D, and it’s interesting to find out that this vitamin may also be considered a hormone. Its activity and synthesis have the ability to occur in various locations in the organism.

Vitamin D also has an essential part to play in the metabolism of calcium and also in the homeostatic processes, and this means it is crucial for our bones’ health. The liver converts vitamin D3 into calcifediol and vitamin D2 into 25-hydroxyergocalciferol.

Then, the kidneys convert a certain amount of calcifediol into calcitriol – vitamin’s D biologically active form. Calcitriol runs as a hormone in the bloodstream, optimizing the levels of phosphate and calcium and promoting healthy bones. Calcitriol is also essential for its ability to regulate immunity and neuromuscular processes.[1]

Vitamin D Deficiency

The deficit of vitamin D has become a worldwide health issue in older people, remaining a common problem in adults and children as well.

Symptoms and health complications of vitamin D deficiency

  1. Rickets

Rickets is a disease that develops during childhood that is manifested as the children start to walk. The symptoms include deforming, weakening and softening of the bones. The longs bones also start bending under the children’s body weight. The dietary risk factors for this illness include the lack of animal foods from the diet.

  1. Osteomalacia

This is a disease that occurs in adult individuals, and it is also caused by the deficit of vitamin D. The symptoms of this health issue includes soft bones which cause the bending of the spine, fragile bones, bow legs, an increased risk of bone fracture and weak muscles.

  1. Diabetes

A review article published in 2016 has reported the fact that vitamin D deficiency may also represent a risk factor for the development of diabetes.

  1. Cancer

Cancer and exposure to the sun are unfortunately linked to the risk of skin cancer and the issues involving this subject. For instance, UVB radiation is the greatest risk factor for the development of nonmelanoma skin cancer.

On the other hand, we already know that the sun represents the main source of vitamin D and that’s why researchers and scientists are studying hard to understand its role in skin cancer. Some specialists believe that enough exposure to the sun will be able to keep the levels of vitamin D in normal limits and, at the same time, to protect the skin from getting damaged. This means that certain sun exposure is beneficial to skin cancer survival.

More research proved that low levels of vitamin D can cause the development of other cancer types including prostate, colon and breast cancer.

  1. Cardiovascular disease

Vitamin D deficiency is also connected to increased risk for some heart-related health problems, such as high levels of cholesterol, hypertension, heart failure, myocardial issues, stroke and more.

  1. Infections

Vitamin D deficit can also lead to some respiratory infections especially during winter when our immunity is lower. Research has already proven the connection between the levels of vitamin D from the body and higher risk for lower and also upper respiratory tract issues. Low levels of vitamin D can also lead to the developing of urinary tract infections and also to pneumonia.

  1. Depression

An existing connection between lack of sunlight exposure and depressive states was noticed millennia ago. Vitamin D can optimize the levels of adrenaline and protect against low levels of serotonin and dopamine, two substances that are responsible for our mental wellbeing.

  1. Multiple sclerosis

Low levels of vitamin D in the body lead to higher risks for developing the severe health issue called multiple sclerosis.

  1. Tuberculosis

Studies have linked the existence of tuberculosis in some individuals with lower levels of vitamin D, compared to healthy people.

  1. Inflammation

It has been proved that increased levels of vitamin D lead to decreased levels of inflammation markers found in the blood.

  1. Allergies

Research has shown that the development of certain allergies is linked with low vitamin D levels.

  1. Sleep apnea

Studies have offered evidence that vitamin D deficiency can increase the risk of developing obstructive sleep apnea caused by inflammatory rhinitis.

  1. Dental cavities

Low levels of vitamin D can lead to dental cavities especially in children.

  1. Excessive sweating

Excessive sweating, while your activity levels are low, can suggest a sign that you have vitamin D deficiency.

  1. Unexpected weakness

If you have a vitamin D deficiency, this issue can cause a feeling of over exhaustion even if you are not tired and if you are getting enough sleep.

Diagnosing Vitamin D Deficiency

In order to be able to determine if you suffer from vitamin D deficiency, your doctor will start by taking your health history to see if you have any of the symptoms that describe vitamin D deficiency. The specialist will most likely order a blood test for the serum concentration of 25(OH)D – this is the type of vitamin D that circulates in the bloodstream and it is considered the optimal reflection of how much vitamin D you have taken from various foods and absorbed from exposure to sunlight.

The levels of vitamin D are expressed in nanomoles/liter (nmol/L) or in nanograms/milliliter (ng/mL). According to ODS (Office of Dietary Supplements), the results from the blood test can show the following situations:

  • Less than 30 nmol/L – this means you are deficient in vitamin D
  • Between 30 nmol/L and 50 nmol/L – this indicates a potential vitamin D deficiency
  • Between 50 nmol/L and 125 nmol/L – if you are in these limits, it means that you have normal levels of vitamin D in the blood
  • Higher than 125 nmol/L – this shows high levels of vitamin D

Causes of vitamin D deficiency

Limited exposure to the sun

According to research, the prevalence of vitamin D deficiency is increased even in climates with sunny weather. As we’ve said before, exposure to the sun is connected with the dangers of skin cancer, that’s why we are advised to use sunscreen to be protected. But what we didn’t know until now is that such preventative actions like using sunscreen will decrease the levels of vitamin D from our body. Because sunscreen protects very well against UVB rays and also that a sunscreen with an SPF of 30 can reduce vitamin D synthesis in the skin by 95%, it’s pretty obvious that it can cause vitamin D deficiency.

On the other hand, we also tend to spend most of our time indoor therefore we cannot meet the vitamin D needs through exposure to sunlight alone.

Some studies conducted by the National Cancer Council in Australia showed how to minimize the risk for skin cancer while maintaining optimal levels of vitamin D from exposure to the sun. It seems that when the UV index is 3 or higher, extended exposure to the sun without any protection is prohibited. But, when the UV index is below 3, specialists recommend that we go outside in the middle of the day without having to worry about protection against the sun rays.

Skin pigmentation

According to scientific research, dark skinned people have lower vitamin D levels; they are less efficient in making it because the melanin from their skin inhibits vitamin D synthesis.

Overweight and obesity

Being obese or overweight can also cause a higher risk for vitamin D deficiency. Fat cells extract vitamin D from the blood, and they also alter its release into blood circulation. Individuals with a BMI of 30 or higher will usually also manifest vitamin D deficiency.

Consuming low levels of vitamin D over time

For instance, if you follow a strict vegan/vegetarian diet, you might be at a high risk for vitamin D deficiency, since most vitamin D sources are animal-based.

Kidney issues concerning the conversion of vitamin D to its active form

As we age, our kidneys will start having problems when they try to convert vitamin D to its active form, and this leads to an increased risk of vitamin D in older adults.

The digestive tract cannot absorb vitamin D in an optimal way.

Certain health issues will inhibit the intestine’s ability to absorb vitamin D from the food we consume.

Risk factors for vitamin D deficiency


Individuals who suffer from one of the many malabsorption syndromes such as celiac disease are usually unable to absorb an optimal quantity of vitamin D in their body.


Children: children between the ages 11-18 are more likely to be overweight or obese and also to be vitamin D deficient.

Elder people: their body’s ability to synthesize vitamin D from the sun decreases and so does their ability to absorb it from food.

Rheumatoid arthritis

A study analyzed 1143 patients with this health issue, and the results showed that the majority of them were also vitamin D deficient.


The exact connection between this condition and the deficit of vitamin D from the body is not yet entirely known, but scientific evidence shows that people with fibromyalgia also suffer from vitamin D deficiency.

Certain medical conditions and treatments

The breakdown of vitamin D can be enhanced by quite a large variety of medications including anticonvulsants, antifungal drugs, glucocorticoids, AIDS/HIV treatment and more.

Advice for reversing/preventing vitamin D deficiency

  1. Spend more time outdoor, in the sun.

The recommended exposure to sunlight should be around 10-30 minutes every day.

  1. Take vitamin D supplements.

Supplementing with vitamin D is the easiest and the most efficient way to optimize your vitamin D levels.

  1. Remember that D3 is the most readily absorbable form of vitamin D.

After a couple of months of taking vitamin D supplements, it’s recommended that you run a 25-hydroxy vitamin D blood test, to make sure you’re not overdosing. After you get the results, you should adjust your vitamin D3 according to them.

  1. Eat foods with a composition rich in vitamin D!

The most important ones include the following:

  • Salmon, herring, sardines
  • Cod liver oil
  • Canned tuna
  • Oysters
  • Shrimp
  • Egg yolks
  • Mushrooms
  • Fortified foods (cow’s milk, soy milk, orange juice, instant oatmeal, cheese, almond milk, yogurt)

Vitamin D Science-Based Health Benefits 

  1. Improves bone health.

Vitamin D plays a crucial role in our bones’ health. The reason is the fact that it promotes and stimulates the absorption of calcium and phosphorus from the foods we eat. These two are essential nutrients for the skeleton.

Supplementing with vitamin D elder people can diminish the risk of bone fractures and it can also improve healing.

  1. Reduces the risk of diabetes.

Vitamin D can decrease the risk for both types of diabetes: type 1 which is an autoimmune disease usually diagnosed in childhood/adolescence and type 2 occurs later in life, and it’s often related to poor lifestyle.

Infants and toddlers who supplement on vitamin D will have a lower risk of developing the disease. Scientists believe that vitamin D also protects against type 2 diabetes by reducing insulin resistance, increasing insulin sensitivity and also enhancing functions of the cells that produce insulin.

  1. Optimizes the heart’s health.

Vitamin D improves the overall cardiovascular health and supplementation with it will result in a significant decrease of the risks for various heart diseases.

  1. Lowers the chances of developing certain cancers.

Optimal levels of vitamin D can prevent some types of cancers, and evidence shows that it can slow down the progression of this severe disease. Two recent studies have proved that individuals with proper levels of vitamin D have up to 25% lower risk of developing bladder cancer. Having normal levels of vitamin D in the body will also reduce the risk of colorectal cancer.

  1. Reduces the risk of premature death.

Vitamin D can promote a longer and also a healthier life. A couple of studies have described the remarkable link between the levels of vitamin D in the body and the risk of premature death. The results showed that getting enough vitamin D through sun exposure, diet or supplements will definitely add more healthy years to your life.

  1. Combats the symptoms of depression.

Researchers have discovered that vitamin D can also help in case of depression. Scientists have a theory suggesting that vitamin D increases serotonin levels in the brain and therefore it contributes to feelings of happiness and well-being.

  1. Increases muscle strength

Recent research has proven that there are certain connections between the levels of vitamin D and muscle strength in adult individuals and also in elder people. Some studies also confirmed that athletic and non-athletic adults who supplemented on vitamin D had increased body strength.

  1. Can prevent and also treat multiple sclerosis.

Multiple sclerosis represents an autoimmune disease that involves the brain, the spinal cord, and the eyes’ optic nerves. Scientific research suggests that optimizing the levels of vitamin D in the body leads to lower risk of developing multiple sclerosis. It’s also great that individuals who already have this health condition and supplement on vitamin D can slow down the progression of the illness.

  1. Boosts weight loss.

Adding vitamin D supplements to your everyday diet if you are trying to lose some excess weight will show great results. Research has shown that taking daily doses of calcium and vitamin D will lead to faster weight loss and appetite suppression.

  1. Promotes a healthy pregnancy and birth.

Pregnant women who are deficient in vitamin D seem to be exposed to greater risks of developing preeclampsia and therefore they’ll need a cesarean intervention. Low levels of vitamin D are also connected to gestational diabetes and to bacterial vaginosis in women who are carrying a child. Pregnant women should take vitamin D supplements because this will result in lots of benefits for the baby.

  1. Reduces the risk of asthma attacks.

It has been proved that daily doses of vitamin D will diminish the risk of developing asthma in children.

  1. Prevents flu and common cold

If you start taking vitamin D supplements, you will be able to reduce the risk of upper respiratory tract infections.

  1. Improves and speeds recovery after surgery.

Studies and research have shown that optimizing the levels of vitamin D in the body will lead to an enhanced recovery after surgery.

  1. Reduces chronic pain.

In most individuals, healthy levels of vitamin D will combat pain.

  1. Protects against Parkinson’s disease.

Higher levels of vitamin D can reduce the risk of developing the terrible Parkinson’s disease.

  1. Reduces age-related mental decline.

Taking vitamin D supplements will decrease the risk of mental decline, especially among older individuals.[3](

Vitamin D Excess and Possible Side Effects

Toxicity of vitamin D is usually rare, and it is caused by supplementing with high doses. Vitamin D excess is not caused by staying too long in the sunlight.

Individuals who have a specific medical health issue (for instance, hyperparathyroidism) have also higher sensitivity to vitamin D, and they tend to become diagnosed with hypercalcemia due to high levels of the vitamin in the organism. Hypercalcemia during pregnancy may have dangerous effects: it can increase the fetus’ sensitivity to vitamin D’s effects, and it can also lead to the development of facial deformities or even to the mental retardation of the newborn.

The effects of vitamin D excess/overdose include the following:

  • Vomiting and nausea
  • Anorexia
  • Polydipsia and polyuria
  • A state of overall weakness
  • Insomnia
  • Pruritus
  • Renal failure
  • Nervousness

Vitamin D should be safe when it is taken carefully and in the right doses, by mouth, or when it is given as a shot into your muscles, also in the proper recommended amounts. Most users will not experience and side effects unless they overdose. Other symptoms of vitamin D overdose include the following:

  • Fatigue
  • Headache
  • Constant sleepiness
  • Dry mouth
  • Appetite loss
  • Metallic taste in the mouth

If you take vitamin D for very extended periods and also in higher doses than recommended, it is possible that it will cause excessively high levels of calcium in the body.

Special Warnings and Precautions

Pregnancy and breastfeeding: when used in the proper doses recommended by the doctor, vitamin D is safe during pregnancy and breastfeeding.

Kidney disease: Vitamin D can increase calcium levels in the blood, and it can also enhance the risk of hardening of the arteries in individuals who suffer from severe kidney issues. When the kidneys can no longer maintain optimal levels of phosphorous and calcium in the blood, the result will be the development of a bone disease known as renal osteodystrophy. All patients who suffer from this illness must be carefully monitored in order to get their calcium levels checked periodically.

The fact that consuming vitamin D can lead to high calcium levels in the blood can affect in a negative way people who are suffering from the following health conditions:

  • Atherosclerosis
  • Sarcoidosis
  • Histoplasmosis
  • Over-active parathyroid gland
  • Tuberculosis
  • Lymphoma

Optimal Daily Intake of Vitamin D

The subject revolving around the proper intake of vitamin D per day for maintaining the body’s healthy functions is a very controversial one, and many debates involve the issue.

Recent studies and scientific research have shown that our body needs more vitamin D than we once thought was enough. The Institute of Food and Agricultural Sciences have reported some new recommendations about vitamin D necessary daily intake, and these are based on international units (IUs) per day. IUs represent a standard type of measurement used in case of vitamins and drugs with the goal of helping experts and specialists to determine the recommended intake, the toxicity and also possible deficiency levels for each individual.[4]

It is important to remember that one IU is not the same for all types of vitamins; an IU is determined by how much substance it takes to produce some effects inside the organism.

The necessary IUs for vitamin D are the following:

  • Children and teens need about 600 IUs of vitamin D every day
  • Adults up to age 70 also need around 600 IUs of vitamin D every day
  • Adults over the age of 70 need 800 IUs of vitamin D every day
  • Pregnant and breastfeeding women need 600 IUs of vitamin D every day

No matter what, you are advised to talk to your doctor to get the best possible guidance before you decide to start supplementing with vitamin D.


As we’ve seen, vitamin D plays many essential roles in our body and maintaining adequate levels – whether through supplements, food or sun exposure – is crucial for our health. Because it’s quite common for people to be vitamin D deficient without even knowing it, it’s a good idea to get our vitamin D levels checked by a doctor now and then[5][6][7][8]