Vitamin D is produced by the body in response to sunlight exposure, and is crucial for bone health and immune system functioning. Unfortunately, a large portion of the population may be deficient in this sunshine vitamin. To combat this, experts recommend taking a Vitamin D supplement, with Vitamin D3 being the preferred form due to its better bioavailability.
Vitamin D deficiency used to be a rare condition until the industrial revolution. However, by the end of the 19th century, it was estimated that over 90% of children who lived in cities suffered from severe deficiency and rickets (1).
Only then it was discovered that vitamin D deficiency occurs due to inadequate exposure to direct sunlight and leads to debilitating complications such as rickets. Nowadays, rickets in children can be successfully prevented.
Yet, adults spend more time inside than ever before. This sedentary lifestyle leads to an increased incidence of vitamin D deficiency and, as a result, scientists report that the condition currently affects about 50% of the world population (2).
Unless you spend time under the sun daily, it's likely that your vitamin D levels are insufficient, especially during the winter months.
Not to mention that there are only a few good food sources as an alternative and their vitamin D content varies widely. Therefore, experts all over the world recommend supplementation with vitamin D.
In this article, you will find all you need to know about the best way to get enough vitamin D and how to correct your deficiencies quickly, safely, and effectively.
What is vitamin D?
The sunshine vitamin is one of the first hormonal substances produced by a living organism. According to scientists, protozoa started to synthesize it 750 million years ago.
It is often called a prohormone since you can produce it on your own and the diet is not the only source, unlike most other vitamins.
Vitamin D is actually a combination of several fat-soluble vitamins, with the most notable ones being D2 and D3.
Vitamin D3 forms in your skin under the effect of direct sunlight which breaks down one of the cholesterol precursors. In addition, many animals as well as algae can also produce vitamin D3.
On the other hand, vitamin D2 is produced only in plants. Therefore, depending on whether a food source is of plant or animal origin, it may contain either D2 or D3.
What causes vitamin D to drop?
The increasingly sedentary lifestyle of modern people is currently the main cause of low vitamin D levels.
Aspects that contribute to staying more indoors also include the COVID-19 pandemic and the increased use of modern technologies.
Furthermore, the season, as well as the level of air pollution, play a significant role. Vitamin D deficiency is at its highest prevalence during the winter and spring seasons.
All factors that may increase the risk of vitamin D deficiency include:
- time spent indoors
- geographic location and season
- air pollution
- skin color
- excessive use of sunscreen
- medications (corticosteroids, laxatives, orlistat, etc.)
The best way to know whether you have a deficiency or not is to get a vitamin D test from a lab. The biomarker for vitamin D status is called 25-hydroxy vitamin D.
According to the Clinical Practice Guideline of the Endocrine Society Task Force, your 25-hydroxy vitamin D levels should be above 30 ng/ml (75 nmol/l) in order to minimize the possible risks of insufficiency (5).
Furthermore, studies indicate that levels below 20 ng/ml (50 nmol/l) suggest deficiency and a high risk of bone fractures and osteomalacia (6).
Levels below 12 ng/ml (30 nmol/l) are considered dangerous because such severe deficiency is a risk factor for various infectious diseases, cancer, and premature death.
What happens when vitamin D is too low?
Almost every cell in the human body has a receptor for Vitamin D (7). Therefore, the majority of your tissues and organs need it to function properly.
Most notably, the vitamin is needed for the intestinal absorption and maintenance of adequate levels of calcium in the blood.
Thus, low vitamin D can lead to insufficient serum calcium levels and bone health problems. In children, low calcium results in problems with bone development, known as rickets.
In adults, the deficiency can lead to osteoporosis and osteomalacia (8, 9). Osteoporosis increases the risk of bone fractures, while osteomalacia stands for "soft bones" and may cause bone pain and disability.
Furthermore, studies have shown that low vitamin D may increase the risk of:
- heart disease and mortality (10, 11)
- autoimmune conditions such as type 1 diabetes (12) and multiple sclerosis (13)
- respiratory infections (14)
- malignancies such as colorectal (15), breast (16), pancreatic (17), and ovarian cancer (18)
- depression (19)
- Parkinson’s (20)
- insulin resistance and type 2 diabetes (21, 22)
- ovarian dysfunction and reduced fertility (23)
- pregnancy problems (24)
Does low vitamin D cause weight gain?
According to the majority of evidence, patients who have lower vitamin D levels end up losing less fat during weight-loss interventions. Therefore, the deficiency may be a risk factor for becoming overweight or obese.
For example, a randomized controlled trial in 218 women showed that those who remained deficient (<32 ng/mL) after supplementation lost less body fat and weight compared to the rest who became replete (25).
Supplementing with vitamin D does not appear to boost weight loss, but correcting a vitamin D deficiency may help you control your body weight.
Another clinical trial in 77 women also did not report significant weight loss while taking vitamin D, but supplementation led to higher body fat mass reduction (26).
What foods are highest in vitamin D?
Unfortunately, there are only a few foods that are naturally good sources of vitamin D. Those include fatty fish, eggs, and mushrooms.
Furthermore, there are foods fortified with vitamin D sources such as fortified cereal, orange juice, cow's milk and milk products. Infant formula also usually contains added vitamin D.
Fish, and especially fatty fish/oily fish, is the most well-known dietary source of vitamin D and essential fatty acids. For example, drinking cod liver oil was one of the first methods to prevent rickets in children. That is the type of fish oil with the highest content of vitamin D
However, cod liver oil is also high in another fat-soluble vitamin - vitamin A (retinol). Only a tablespoon contains over 4 times the recommended dietary intake of retinol and continuous supplementation may lead to toxicity.
Other types of fish that are rich in vitamin D include salmon, herring, sardines, mackerel, and tuna.
Salmon is usually the better choice since it is much lower in mercury than some species of mackerel and tuna.
Yet studies report that there is a huge difference between wild and farmed salmon in terms of vitamin D content - farmed salmon has 4 times lower levels of vitamin D (30).
Eggs and more specifically egg yolks also contain some amounts of vitamin D. However, the levels heavily depend on the method for raising the chickens as well as their diet.
Studies have shown that even when the chickens are given feed with the same amount of vitamin D, the chickens roaming freely outside had 3-4 times higher vitamin D content in their eggs (31).
Therefore, consuming whole eggs from free-range chickens may also be an efficient way to boost your vitamin D intake.
If you have concerns about your cholesterol levels, then make sure to consult with your doctor before increasing your egg yolk intake. Research has shown that increasing dietary intake of cholesterol does not affect blood cholesterol levels in most people.
Studies suggest that only 15-25% of individuals are cholesterol hyperresponders and consuming more cholesterol will cause changes in their lipid profile (32). Even if you are one, scientists do not report increased cardiovascular risk in hyperresponders.
Mushrooms are also an excellent source of vitamin D. However, the levels of the vitamin depend heavily on whether they are wild or farmed mushrooms as well as the method of farming.
Unfortunately, most mushrooms are farmed in darkness, which completely deprives them of any vitamin D. On the other hand, consuming wild mushrooms hides risks of poisoning.
According to studies, modern farming methods using UV light may increase vitamin D content in mushrooms to levels equivalent to those in wild mushrooms (33).
What is the most reliable source of vitamin D?
The most natural way to increase your vitamin D levels is via exposure to direct sunlight. However, the method is often unreliable due to various factors including season, genetics, age, etc.
Furthermore, excessive exposure to sunlight is an increased risk factor for serious conditions such as skin cancer because of UV exposure.
Considering the highly variable amounts of vitamin D in different food sources as well as the high incidence of vitamin D deficiency, it's widely recommended by experts to take a vitamin D supplement (34).
Currently, there are two main forms of vitamin D available as a supplement - vitamin D3 and vitamin D2
According to a meta-analysis of 7 studies, vitamin D3 (known as the active form of vitamin D: cholecalciferol) has better bioavailability than vitamin D2 and leads to a more reliable increase of serum concentrations (35).
Furthermore, D2 appears to be a less stable form of the vitamin and therefore researchers suggest that it may have reduced shelf-life as a supplement (36).
Therefore, the majority of experts recommend supplementing with vitamin D3 in order to increase serum levels more reliably.
What is the best way to absorb vitamin D?
Vitamin D supplementation is effective only if the supplement is properly absorbed. In order to boost vitamin D absorption, you should do 3 things:
- take it with a meal rich in healthy fats, as vitamin D is a fat-soluble vitamin
- avoid foods and drugs that block the absorption of the vitamin
- pick a more absorbable form
Taking the vitamin with a meal rich in healthy fats ensures the release of bile acids into your digestive tract which is important for the proper absorption of vitamin D.
Therefore most experts recommend taking a vitamin D supplement with the largest meal of the day which is lunch or dinner for most people.
What blocks the absorption of vitamin D?
Fiber is an important part of every healthy diet as it helps digestion, lowers cholesterol, improves blood sugar control, and reduces the risk of colon cancer.
However, it's important to avoid taking vitamin D with other supplements that may contain fiber, such as many products for weight loss and digestion.
Furthermore, prolonged use of several medications may lead to reduced absorption or changes in the metabolism of vitamin D and, therefore, a deficiency. Examples are:
- Laxatives (bisacodyl)
- Cholesterol-lowering drugs (such as cholestyramine and colestipol)
- Seizure-control drugs (such as phenobarbital and phenytoin)
- Anti-tuberculosis drug (rifampin)
- Weight-loss drugs (orlistat)
How can I raise my vitamin D level quickly?
The most reliable source of vitamin D that can help you raise your serum levels quickly is a vitamin D3 supplement. The majority of guidelines recommend supplementing with at least 15mcg (600 IU) daily (37, 38, 39).
However, these levels may be insufficient for most people to achieve adequate levels of serum vitamin D if they are severely deficient. Therefore most experts recommend 1 000 to 4 000 IU of the vitamin per day.
In addition to daily supplementation, taking a bolus dose of vitamin D once a week or even once a month is also an option.
According to studies, the method may lead to a prolonged increase in serum vitamin D levels. However, daily supplementation appears to cause comparable increases which occur faster than a single bolus (40).
Therefore you should go for daily dosing if you want to correct your deficiency faster.
Furthermore, researchers report that the physiologic limit of vitamin D is 10 000 IU per day, which is equal to prolonged whole-body exposure to direct sunlight (41).
Taking 10 000 IU of Vitamin D or more may be toxic. Toxicity is considered to occur in cases of supplementation with doses above 10 000 IU per day for longer than 3 months or more than 300 000 IU for 24 hours (42).
How long does it take to correct a vitamin D deficiency?
The dose and the form of your supplement are not the only factors that will determine how quickly you may replenish your vitamin D levels.
According to scientists, the period required to correct a vitamin D deficiency depends on several factors (42). They include:
- your baseline vitamin D levels
- your age
- season and sun exposure
- your skin pigmentation
- genetic variations
- whether you are taking any medications
- your body fat and composition
- your overall diet
Therefore, make sure to measure your vitamin D levels through a blood test and consult with your doctor first. Depending on your baseline vitamin D levels and the rest of the factors above a physician can estimate the most optimal dosage for you.
Which vitamin D is best?
When choosing a supplement, it's best to pick a product with both vitamin D3 and vitamin K2 such as the AdaptoZen Vitamin D3 + K2 Drops by Nutririse.
Vitamin K is another group of fat-soluble vitamins which plays an important role in the human body. These vitamins control blood coagulation as well as the deposition of calcium in different tissues, including bones.
According to studies, a combination of vitamin D3 and K2 may have a synergistic benefit for bone mass density (43).
Furthermore, vitamin K2 may reduce the risk of calcium depositing in your blood vessels, which is a potential risk factor for cardiovascular disease. Therefore, the combination of vitamin D3 and vitamin K2 will help direct the calcium to your bones.
You can stay assured that the contents inside the Vitamin D3 + K2 supplement match the label 100% thanks to the extensive testing and 3rd party quality control.
Each batch is tested 3 times during the manufacturing process and then a 4th time by an independent 3rd party organization.
All ingredients are non-GMO and this D3 supplement is free of gelatin, gluten, dairy products, artificial preservatives, harmful binders and fillers, artificial colors, and flavors.
Besides, all Nutririse supplements are manufactured in US-based, GMP-certified facilities.
Note: This article is for informational purposes only, and not intended for use as medical advice. Always consult your primary care provider before starting any dietary supplement.