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What Happens to Your Body When You Take Vitamin D

Everything to know about Vitamin D from experts.
FACT CHECKED BY Emilia Paluszek

Vitamin D is an essential thing we need to maintain overall good health. It's crucial for many things including strong bones, brain health and strengthening your immune system. According to the Mayo Clinic, "the recommended daily amount of vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for people ages 1 to 70 years, and 800 IU for people over 70 years."  If you can't get a few minutes of sun everyday, which is a good source of vitamin D, there's plenty of other ways. Dr. Naheed A. Ali, MD, PhD with USA RX tells us, "The good news is that vitamin D is available in a number of forms — both supplements and fortified foods." He adds, "Everyone needs vitamin D to stay healthy…It helps your body absorb calcium and phosphate, two minerals that are important for healthy bones and teeth. It also helps your body absorb some vitamin K, a crucial vitamin for blood clotting." Eat This, Not That! Health spoke with experts who explain everything to know about vitamin D and why it's something everyone needs. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Why Vitamin D is Important

Shot of a doctor explaining a medical procedure with a model to a senior patient while sitting in her office

Dr. Jacob Hascalovici, the Chief Medical Officer with Clearing, a telehealth platform for chronic pain patients states, "Vitamin D matters because it assists with calcium and phosphorus intake and retention, which is important for healthy bones. We are still learning other ways vitamin D helps, though initial studies indicate that it could be involved with managing inflammation and restricting cancer cell growth." 

​​Dr. Suzanna Wong. a licensed Doctor of Chiropractic and health expert with Twin Waves Wellness says, "Vitamin D works like a hormone – it has receptors in every cell in the body – which makes it one of the most important vitamins you can take. It helps with the following:  forming strong bones, muscle strength, immune function, brain health (anxiety and depression especially), some cancers, diabetes, and weight loss and preventing osteomalacia."

Gita Castallian, MPH Public Health Analyst at The California Center for Functional Medicine explains, "Vitamin D is an essential nutrient that helps us to absorb calcium and promote bone growth. Vitamin D additionally regulates many cellular functions of the body. It is an anti-inflammatory antioxidant with neuroprotective properties that support muscle function, brain cell function and immune health. As we saw during the COVID pandemic, an individual's Vitamin D level was very important for determining whether they might be more susceptible and more likely to experience serious symptoms with COVID-19."

Dr. Ali says, "Vitamin D is a natural steroid hormone produced by the body. It plays a number of important roles in the body, including regulating glucose and fat metabolism. Adequate levels of vitamin D are necessary for maintaining good health. Vitamin D helps your body absorb calcium and phosphate from the intestines and bones, helps your body produce endocannabinoid (a regulating substance) which interferes with the endocannabinoid system (Native American specific), and helps your body absorb other vitamins and minerals."


What Happens When You Lack Vitamin D and How to Avoid a Deficiency

Thoughtful girl sitting on sill embracing knees looking at window, sad depressed teenager spending time alone at home, young upset pensive woman feeling lonely or frustrated thinking about problems

Dr. Hascalovici shares, "Vitamin D deficiency can lead to brittle bones (osteoporosis) and more frequent fractures. Tiredness, weakness, depression, and pain can be other signs of vitamin D imbalances."

Dr. Wong adds, "When you lack Vitamin D you probably won't notice to start with  – around 50% of the population are deficient. A blood  test is needed to see what your levels are – but with children you start to see bowed legs form (rickets) and in adults all of the above areas can start to present when your levels are low. The easiest way to avoid deficiency is to take a supplement (4000iu a day) and spend as much time outdoors in the sun as possible."

Dr. Ali shares, "The amount of vitamin D you should take will vary depending on your age, weight, and health. Most people should take vitamin D3 or D5 supplements. If you are over 50 years old, you may wish to consider taking a vitamin D2 or a vitamin K2 supplement. If you are a child or an adult with a good diet, you do not need to take high amounts of vitamin D. Adolescents and teens with a poor diet can get by with low amounts of vitamin D."


Best Ways to Get Vitamin D

Sunlight in the green forest, spring time

Dr. Hascalovici says, "Many of us can get vitamin D through (limited) exposure to sunlight. Though using sunscreen is important and is normally recommended, many of us can get enough vitamin D by spending 15 to 30 minutes in sunlight, often around midday. The amount of sunlight you need will depend on factors such as your skin pigmentation, where you live, and whether you are predisposed to skin cancer. Food is another source of vitamin D, including tuna, egg yolks, yogurt, dairy milk, fortified cereals, raw mushrooms, or orange juice. A supplement can also help, though it may not be the only answer."

Castallian and Megan Anderson, APN Nurse Practitioner at The California Center for Functional Medicine  add, "You can get Vitamin D in many ways, including the foods you eat, nutritional supplements, and sun exposure. While there is no uniform consensus of how much vitamin D people require, at the California Center for Functional Medicine, "we recommend that our patients  have their Vitamin D levels checked at least twice per year, and we consider an optimal range to be between 40-70 for immune system health and cancer prevention. We find that it is very challenging to maintain adequate Vitamin D levels without regular sun exposure and also combined with adequate supplementation. To be honest, many people live far enough from the equator that supplementation is necessary for most people. This is based on our own assessment of our patients' Vitamin D levels when they are not supplementing.

For daily sun exposure and food intake, we recommend:

15-20 minutes at least 3 days per week of sun exposure – aim for mid-day sun exposure. This is when UVB rays (which are required to synthesize vitamin D) are at their strongest. In other words, this is when you can make maximum vitamin D with minimum sun exposure. The best naturally Vitamin D-rich food sources include fatty fish and fish liver oils, egg yolks and beef liver. Many foods and supplements are fortified with Vitamin D as well.  Key whole-food sources include cod-liver oil (which delivers 1,360 IU per tablespoon); fatty fish like canned salmon, sardines, and mackerel (350–920 IU per serving); and eggs (48 IU per egg). Most people require somewhere between 2000-5000 IU of Vitamin D3/K2 supplementation to achieve the optimal range of 40-70."


What to Know Before Taking Vitamin D Supplements

woman taking vitamin D3

According to Dr. Hascalovici, "Whatever combination of vitamin D sources you choose, know that for most adults, between 600 and 1,000 IU per day is around the right amount. Everyone's intake can vary depending on their skin, where they live, and how long they spend outdoors, so a physician or nutritionist can provide more specific guidance." 

Anderson says, "Before starting on a Vitamin D supplement, it's important to know what your level is without supplementation.  By knowing that, your healthcare provider can make a more targeted recommendation. If your level is below 30, we normally recommend starting with 5000 IU of Vitamin D3/K2 per day and then retesting in 90 days.  If your level is below 20, we might recommend a higher dosage of 10,000 IU per day for 30-45 days and then dropping down to 5000 IU daily after that.  It honestly is such an individual dance of testing and then supplementing and then re-testing again to figure out what each person's needs might be.  I recommend testing at least twice per year – once after winter when sun exposure has likely been less and then again after summer. By knowing those two levels at different times of the year, you can supplement appropriately."


Pros of Taking a Vitamin D Supplement

Smiling young lady looking at her vitamins

Dr. Hascalovici explains, "The benefits of vitamin D intake include protecting your bones, potentially helping stabilize your mood, and possibly fighting cancer. It's clear that vitamin D is essential and that the body suffers if you do not get enough of it." 

Dr. Wong shares, "The benefits include a stronger immune system, protecting bone and muscle health, protecting against anxiety and depression, better blood sugar management – meaning less risk of diabetes, helps with some cancers."


Cons of Taking Vitamin D


Dr. Hascalovici reminds us, "It's important not to exceed 4,000 IU per day, as too much vitamin D can contribute to nausea, vomiting, kidney stones, heart damage, and cancer.. In rare cases, vitamin D build up over time can lead to calcium-related toxicity." 

According to Castallian and Anderson, "As a whole, appropriate amounts of Vitamin D are highly recommended. However, if you are taking too much Vitamin D in supplement form, some negative effects can arise, including:

Poor appetite and weight loss



Kidney stones/kidney damage

Confusion and disorientation

Heart rhythm problems

Nausea and vomiting

In general, once levels get above 80, it's time to back off supplementation.  This is not the case where more is always better."


Experts Insight About Vitamin D

middle-aged man chatting with doctor

Dr. Hascalovici says, "Vitamin D helps with many functions throughout the body, and it's important to get the minimum recommended amount per day. It's worth strategizing the best way to make that happen for you personally, particularly if you have dark skin, live far from the equator, or have concerns about your calcium intake."

Dr. Ali states, "One of the best things about vitamin D is that it is not only a nutrient but also a natural compound. Getting the recommended amount of vitamin D is easy, and it does not seem to cause any side effects. Getting the amount you need may not be necessary, especially if you are adequately nourished. In fact, people who are underfed and under housed are at risk of vitamin D deficiency. And this can be a precursor to other problems such as rickets, osteoporosis, and diabetes."

Heather Newgen
Heather Newgen has two decades of experience reporting and writing about health, fitness, entertainment and travel. Heather currently freelances for several publications. Read more about Heather