---
title: "Vitamin D: Why You’re Probably Not Getting Enough (and What to Do About It)"
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canonical_url: "https://www.drdanwool.com/blog/vitamin-d"
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lastmod: "2025-07-22T13:00:00.000Z"
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Medically reviewed by [Dr. Dan Wool, NMD](https://www.linkedin.com/in/drdanwool/)

 Arizona-licensed Naturopathic Physician and  Gastroenterology Specialist

 Updated: November 11, 2025

Summary: 

- Why Vitamin D is Essential for Health: Vitamin D functions like a hormone, synthesized from cholesterol in skin during sun exposure and activated in liver and kidneys. Beyond regulating calcium and phosphorus absorption for strong bones and teeth, Vitamin D strengthens immune defenses, reduces autoimmune reactions, improves mood and brain health reducing depression and cognitive decline, may prevent certain cancers through cell growth regulation, and supports cardiovascular health by regulating blood pressure and reducing inflammation.
- Common Causes of Vitamin D Deficiency: Over 1 billion people worldwide are Vitamin D deficient due to insufficient sun exposure from indoor lifestyles, sunscreen use blocking UVB synthesis, and northern latitude living. Darker skin pigmentation requires more sun exposure for equal production. Age reduces skin synthesis efficiency, obesity stores Vitamin D in body fat reducing bloodstream availability, and few foods naturally contain Vitamin D including fatty fish, egg yolks, and fortified products insufficient for daily needs.
- Safe Vitamin D Supplementation Guidelines: Recommended daily intake is 600 IU for adults 19-70 and 800 IU for ages 71+ with 4,000 IU upper limit, though experts suggest 1,000-2,000 IU for optimal levels. Vitamin D3 (cholecalciferol) is superior to D2 (ergocalciferol) with better potency, longer duration, and higher bioavailability. Take with fat-containing meals for absorption, combine with Vitamin K2 for calcium metabolism, and monitor through regular 25-hydroxyvitamin D blood testing to prevent toxicity.
- Vitamin D Benefits for Gut and Hormonal Health: Higher Vitamin D levels increase gut microbiome diversity supporting immune function, digestion, and mood regulation while reducing intestinal inflammation and protecting against leaky gut syndrome. For women's health, Vitamin D supports progesterone production for menstrual regularity and fertility, improves PCOS symptoms including ovulation and metabolic markers, and eases menopausal symptoms like mood swings and bone loss making it essential for hormonal balance throughout life stages.

Are you deficient in Vitamin D? Most of my patients are when we first test them. How can that be in sunny Arizona? 

Vitamin D is even called the “sunshine vitamin” as its production is stimulated in the skin when you’re exposed to the sun. It is a fat-soluble nutrient that plays a critical role in bone health, immune function, hormonal balance, and even gut health.

Despite its high importance, Vitamin D deficiency is one of the most common nutrient deficiencies worldwide in our modern age, affecting over 1 billion people globally [1]. Below, the main topics that we’ll explore will answer why Vitamin D is essential, why deficiency is so widespread, how to supplement safely, and what emerging research says about its broader health benefits, including its effects on the microbiome and hormones.

## Why Vitamin D Is So Important?

Vitamin D is unique among vitamins because it functions more like a hormone. It is synthesized from cholesterol in the skin when you are in the sun and is then activated in the liver and kidneys. Its most well-known role is in regulating the absorption of calcium and phosphorus, which is essential for strong bones and teeth [2].

However, the importance and influence of vitamin D reach far beyond the skeletal system to:

Immune support: Vitamin D helps the immune system work smarter by strengthening your body’s natural defenses and calming overreactions that can lead to autoimmune issues. Here are key areas of overall health influenced by Vitamin D. 

- Mood and brain health: Low levels of Vitamin D are often linked to depression, seasonal affective disorder, and cognitive decline.
- Cancer prevention: Some studies suggest that adequate Vitamin D levels may reduce the risk of certain cancers by regulating cell growth and differentiation.
- Cardiovascular health: Vitamin D may help regulate blood pressure and reduce inflammation, both of which are factors that put you at risk for heart disease.

## Why Most People Nowadays Are Vitamin D Deficient

Despite the body’s ability to produce Vitamin D from sunlight, deficiency is alarmingly common in recent years. Below are the main contributing factors [1]:

- Insufficient Sun Exposure - Modern lifestyles often involve spending a lot of time indoors. Even when outside, we use sunscreen and clothing to protect from harmful UVB exposure, which is necessary for Vitamin D synthesis. (Many slather it on before even leaving the house.) Add to that the fact that a significant part of the Western population lives in northern latitudes where sunshine is not enough, and the result is a limited amount of sunshine for most people.
- Skin Pigmentation - Melanin reduces the skin’s ability to produce Vitamin D. People with darker skin require more sun exposure to generate the same amount of Vitamin D as those with lighter skin, and in many countries and climates, they’re not getting enough sun exposure either, due to the predominant indoor lifestyle.
- Age - Our skin becomes less efficient at synthesizing Vitamin D as we age. Older adults are particularly at risk for deficiency.
- Obesity - Because Vitamin D is stored in body fat, people with higher body fat may have less of it available in the bloodstream for their body to use.
- Diet - Very few foods contain Vitamin D naturally. These include fatty fish (like salmon and mackerel), egg yolks, and liver. Fortified foods such as milk, orange juice, and cereals help, but are often not enough to meet your daily needs [2].

## How to Supplement Vitamin D Safely

Vitamin D (along with A, E and K) is a fat soluble vitamin. These can get toxic over time if taken incorrectly. (We saw this during Covid: everyone knew Vitamin D was helpful for immune health and [some overdid it and ended up in the very hospital](https://pmc.ncbi.nlm.nih.gov/articles/PMC8811610/)they were hoping to avoid)  Given the difficulty of obtaining sufficient Vitamin D from natural sources such as food and sunlight alone, supplementation is often necessary. But the question is, how do you know how much is enough, and how much is too much?

According to the US National Institutes of Health, the recommended daily intake is: 

- Adults 19–70 years: 600 IU (15 mcg)
- Adults 71+ years: 800 IU (20 mcg)
- Upper Limit: 4,000 IU (100 mcg) per day [2]

Nevertheless, many experts suggest that these recommendations are still considered low (given the potential risk of toxicity health agencies are conservative to protect the public). The Mayo Clinic, for example, states that 1,000 to 2,000 IU per day is generally safe and may be more effective for achieving optimal blood levels [3].  

Meanwhile, I see 5,000IU maintain healthy levels in labs when regularly taken and tested and I see 10,000IU help correct deficient in 2-3 months when taken and monitored appropriately. So mindfulness, monitoring and knowing the time and place to intervene is important and should be discussed with your naturopathic doctor or functional medicine practitioner.

## Forms of Vitamin D

Two primary forms of Vitamin D are relevant to human health - Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). While both forms are fat-soluble and help maintain bone health and immune function, they differ in origin, potency, and how the body processes them.

Vitamin D2 is extracted from plant sources and fungi, such as mushrooms exposed to ultraviolet light. It is commonly used in prescription supplements and is often the form found in fortified foods like cereals and plant-based milk alternatives. However, studies have shown that Vitamin D2 is less effective at raising and maintaining serum 25-hydroxyvitamin D levels, which is the marker used to assess Vitamin D status when you have a blood test, compared to Vitamin D3.

Vitamin D3, on the other hand, is synthesized in the skin when you’re exposed to sunlight (UVB radiation) and is also found in animal-based foods such as fatty fish, liver, egg yolks, and fortified dairy products. It is the preferred form for supplementation because it is more potent and acts for longer once in your body. Research indicates that Vitamin D3 produces more biologically active compounds and is more efficient at increasing and sustaining circulating Vitamin D levels.

Both types of Vitamin D are absorbed in the small intestine, and this process works even better when you take them with a meal that includes some fat. While your body can use both D2 and D3, Vitamin D3 is more easily processed and tends to stay in your system longer, making it the more effective option.

For most people, especially those taking supplements to deal with a deficiency, Vitamin D3 is the recommended form due to its superior bioavailability and efficacy. However, for individuals following a strict vegan diet, D2 may be a suitable alternative, though it may require more frequent dosing or higher amounts to achieve the same effect. It’s best to consult with a healthcare professional before starting supplements, regardless of whether you’re vegan or not.

## Best Practices with Vitamin D 

To maximize the effectiveness of Vitamin D supplements, it is best to take them with a meal that contains fat, as this enhances their absorption in the body [2]. Combining Vitamin D with Vitamin K2 is also recommended, as K2 plays a crucial role in directing calcium to the bones and away from arteries, thereby supporting calcium metabolism and reducing the risk of arterial calcification.

Additionally, it is important to monitor your Vitamin D status through regular blood testing, most importantly with the 25-hydroxyvitamin D test, which helps tailor your dosage to individual needs. (I cannot stress this enough).

Vitamin D is important for your health, but because it’s stored in body fat, taking too much over time can build up in your system and become harmful. Although it’s rare, getting too much Vitamin D can cause toxicity, which can manifest as feeling sick, weak, or even lead to kidney issues. That’s why it’s important to stick to safe amounts and talk to a healthcare provider if you’re thinking about taking high doses.

## Being Careful: Symptoms and Causes of Vitamin D Toxicity

Vitamin D toxicity (basically overdosing on Vitamin D), while uncommon, can occur when you take significantly more than the recommended levels over an extended period. Symptoms of toxicity may include nausea, vomiting, and a reduced appetite, along with muscle weakness and frequent urination. One of the most serious consequences is hypercalcemia, an abnormally high level of calcium in the blood, which can lead to the formation of kidney stones and the calcification of soft tissues such as the heart and lungs [4]. This condition typically arises from taking more than 10,000 IU of Vitamin D per day for several months. Rest assured that you cannot get Vitamin D toxicity from sun exposure or dietary intake, as the body regulates Vitamin D synthesis from sunlight and food sources naturally. To avoid these risks, it is advised not to exceed the upper intake limit of 4,000 IU per day unless this is done under the close supervision of your healthcare provider.

## Vitamin D and The Microbiome

Recent research points out that Vitamin D may play a significant role in supporting the gut microbiome [5], which is recognized more and more as a key player in healthy immune function, digestion, and even mood regulation. Higher levels of Vitamin D have been associated with increased microbial diversity, meaning better gut health and resilience. This diversity is important because a richer microbiome is better equipped to support immune balance and protect against pathogens. Vitamin D may also help keep your gut healthy by calming inflammation and supporting your immune system. It helps protect the lining of your intestines, which acts like a barrier to keep harmful substances out of your bloodstream. When this barrier is weak, a condition sometimes called 'leaky gut', toxins and bacteria can slip through and cause widespread inflammation. This is especially important for people with a compromised immune system, i.e., with autoimmune or inflammatory conditions, where gut health is often affected. In these cases, Vitamin D might offer extra support as part of a broader wellness plan.

## Vitamin D and Hormonal and Reproductive Health

Vitamin D plays an important role in keeping hormones balanced, especially for women. It helps support the second half of the menstrual cycle by encouraging the body to make more progesterone, a hormone that’s key for regular periods and fertility. Women with conditions like polycystic ovary syndrome (PCOS) often have low Vitamin D levels, and studies show that taking Vitamin D can help improve ovulation and support better blood sugar and cholesterol levels. During menopause, Vitamin D may also help ease common symptoms like mood swings, hot flashes, and bone thinning. Because of these wide-ranging benefits, Vitamin D is often used in natural and holistic approaches to support women’s hormonal health at every stage of life.

For a fuller take from me on Vitamin D, check out this [video](https://www.youtube.com/watch?v=hMsSeXpq878) on my [You Tube Channel ](https://www.youtube.com/channel/UCY63QXgeUwAbzRXK2F6z0sA)which is [summarized here on my blog. ](https://drdanwool.com/blog/vitamindvideo)

## Frequently Asked Questions about Vitamin D

### 1. What are the signs I might be vitamin D deficient?

Common signs include fatigue, bone pain, frequent infections, mood changes, and muscle weakness. Since vitamin D deficiency affects over 1 billion people globally, it's especially prevalent in Scottsdale residents who spend significant time indoors despite sunny weather. A simple blood test measuring 25-hydroxyvitamin D levels can confirm your status and help determine the right supplementation approach for your individual needs.

### 2. How much vitamin D should I take daily?

While standard recommendations suggest 400-800 IU daily, many experts recommend 1,000-2,000 IU for optimal health. Some patients need 5,000 IU for maintenance or 10,000 IU to correct deficiencies. The key is personalized dosing based on blood testing—vitamin D3 is the preferred form, taken with fat-containing meals. Always work with a naturopathic doctor to monitor levels and avoid toxicity.

### 3. Can vitamin D help with hormonal balance and gut health?

Absolutely. Vitamin D supports progesterone production, helping regulate menstrual cycles and fertility. It's particularly beneficial for PCOS patients and menopausal symptoms. For gut health, vitamin D increases microbial diversity, reduces inflammation, and strengthens intestinal barriers to prevent "leaky gut." This makes it valuable for supporting overall immune function and managing autoimmune conditions through natural medicine approaches.

### 4. How do I know if I'm vitamin D deficient?

Common signs include persistent fatigue, frequent infections, bone/muscle pain, mood changes, slow wound healing, and hair loss. However, many people have no obvious symptoms. Only a 25-hydroxyvitamin D blood test confirms deficiency. Most Scottsdale residents are deficient despite sunny weather due to indoor lifestyles and sunscreen use.

### 5. What's the best time to take vitamin D? Do I have to take it with food? 

Take vitamin D3 with your largest meal containing healthy fats (breakfast or dinner) for optimal absorption. Vitamin D is fat-soluble, so pairing it with foods like eggs, avocado, nuts, or olive oil enhances uptake. Morning dosing may be ideal as it aligns with natural sunlight exposure patterns.

## The Bottom Line on Vitamin D

Vitamin D is far more than just a bone-health nutrient. It supports many key processes in the body such as the immune function, hormonal balance, and even gut health. Yet, deficiency remains widespread due to modern lifestyles, limited sun exposure, and inadequate dietary intake. By understanding the signs of deficiency, testing your levels, and supplementing wisely, you can harness the full benefits of this essential nutrient safely and effectively.

About the Author

## Dr. Dan Wool, NMD

Dr. Dan Wool is a naturopathic doctor who specializes in gastroenterology, hormones and men's health in Scottsdale, Arizona. [Set up a free 15-minute discovery call with Dr. Wool today! ](https://drdanwool.com/booking)

[Read more about Dr. Wool's Gut Health Journey](/about)

## References:

[1] [Cleveland Clinic. (2023). Vitamin D Deficiency: Causes, Symptoms & Treatment. https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency ](https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency)

[2][National Institutes of Health. (2023). Vitamin D - Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ ](https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/)

[3[] Mayo Clinic. (2023). How much vitamin D do I need? https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-how-much-vitamin-d-do-i-need/ ](https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-how-much-vitamin-d-do-i-need/)

[4] [Mayo Clinic. (2023). Vitamin D toxicity: What if you get too much? https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108 ](https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108)

[5] [National Institute of Environmental Health Sciences. (2023). Microbiome. https://www.niehs.nih.gov/health/topics/science/microbiome](https://www.niehs.nih.gov/health/topics/science/microbiome)