Let’s talk about vitamin D—often called the “sunshine vitamin,” but here’s a fun fact: vitamin D isn’t really a vitamin at all. It’s a hormone. Or at least, that’s how it functions in the body.

When your skin is exposed to sunlight, it makes a compound that your liver and kidneys then convert into calcitriol, the active hormone form of vitamin D. This hormone travels throughout your body, turning genes on or off, regulating calcium levels, supporting the immune system, and influencing everything from your mood to your muscle function.

So, calling it a “vitamin” is a bit of a misnomer—it’s more like your body’s solar-powered hormone. You can also get it through food and supplements, which is important because many people aren’t getting enough, and that can lead to issues with bone health, immune function, and more.

In this post, we’ll break down what vitamin D does, why it matters, and how to get enough—safely and effectively.

Why Is Vitamin D So Important?

1. Supports Bone Health

Vitamin D helps your body absorb calcium and phosphorus—minerals that are critical for building strong bones and teeth. Without enough vitamin D, the calcium in your diet doesn’t get absorbed properly, and that can lead to:

- - Rickets in children (soft, misshapen bones)
  - Osteomalacia in adults (bone pain and muscle weakness)
  - Osteoporosis in older adults (thin, brittle bones prone to fractures)

For breastfed infants, vitamin D is especially important. Breast milk doesn’t contain enough on its own, so the American Academy of Pediatrics recommends 400 IU of vitamin D3 per day, starting soon after birth. A liquid supplement works well for this.

2. Helps Regulate the Immune System

Vitamin D plays a key role in immune function. It helps immune cells like monocytes and macrophages fight off infections more effectively and reduces chronic inflammation. Low levels have been associated with a higher risk of respiratory infections, autoimmune conditions, and slower recovery from illness.

3. Affects Mood and Cognitive Function

There’s growing evidence linking low vitamin D levels to mood disorders and cognitive changes. Some of the conditions that may be associated include:

- - Depression
  - Seasonal Affective Disorder (SAD)
  - Cognitive decline and dementia, particularly in older adults

Your brain has vitamin D receptors throughout its tissue, which suggests this vitamin is involved in both brain development and ongoing brain function. While vitamin D isn’t a cure-all, optimizing your levels can be one part of a comprehensive plan for emotional and mental health.

4. Supports Heart Health

Although research is still ongoing, studies suggest that vitamin D may help with:

- - Regulating blood pressure
  - Reducing inflammation in blood vessels
  - Protecting against heart failure and stroke

While it’s not a substitute for good lifestyle habits, it may be one more piece of the puzzle in preventing cardiovascular disease.

How Can You Get Enough Vitamin D—Safely?

This is where things get tricky. You want to get enough vitamin D to support your health, but not at the expense of increasing your risk for skin cancer. Let’s look at your best options:

1. Get Some Sun—but Not Too Much

Sunlight is a very effective way to make vitamin D naturally. For many people, about 10 to 15 minutes of midday sun exposure (on the arms, hands, or legs) two to three times per week is enough to maintain healthy levels. That said, more isn’t better—and longer exposure without protection raises your skin cancer risk, especially for fair-skinned individuals.

Smart sun tips:

- - Get brief exposure without sunscreen, then apply sunscreen after 10–15 minutes.
  - Avoid prolonged sun between 10 a.m. and 3 p.m., when UV rays are strongest.
  - Never use tanning beds for vitamin D—they drastically increase your risk of melanoma and are not a safe alternative.

2. Eat Foods Rich in Vitamin D

Sunlight isn’t always reliable—especially in winter or for people who work indoors. Food becomes your next best ally. While not many foods naturally contain vitamin D, a few stand out:

Top sources:

- - Fatty fish (salmon, mackerel, sardines, tuna)
  - Egg yolks
  - Fortified dairy and non-dairy milk
  - Fortified breakfast cereals

Try to include a few of these in your weekly routine, especially during colder or darker months.

3. Consider Supplements (When Needed)

If you’re not getting enough from sunlight or food, supplements are a safe and effective option. The most common and bioavailable form is vitamin D3 (cholecalciferol). The ideal dose depends on your individual needs and current blood levels.

General guidance:

- - Many adults do well with 2,000–5,000 IU daily, but this isn’t a one-size-fits-all recommendation.
  - People with diagnosed deficiency may need higher doses for a short time under medical supervision.
  - Always talk to your healthcare provider before starting or adjusting a supplement.

4. Know Your Risk Factors and Monitor Your Levels

Certain factors can increase your need for vitamin D:

- - Darker skin (which reduces vitamin D production from sunlight)
  - Older age
  - Digestive disorders that impair absorption (like celiac or Crohn’s disease)
  - Use of certain medications (e.g., steroids, seizure medications)

If you fall into any of these categories—or just want to be proactive—consider asking your provider for a vitamin D blood test. This helps determine whether you need a supplement and what dose is right for you.

If you have a personal or family history of skin cancer, or you’re especially fair-skinned or prone to sunburns, we recommend leaning more on food and supplements and less on direct sun exposure. Regular skin checks with a dermatologist are also a good idea.

Bottom Line

Vitamin D is more than just a nutrient—it’s a foundational piece of your health. From bone strength to immune resilience, mood regulation, and even cardiovascular support, it plays a central role in how your body functions and feels.

You don’t need to overexpose yourself to sunlight to get enough. A thoughtful combination of short, safe sun exposure, a nutrient-rich diet, and supplementation when necessary can help you maintain optimal levels without increasing your skin cancer risk.

If you’re not sure where you stand, a quick conversation with your healthcare provider and a simple blood test can go a long way.

This blog post was written by Katey Perry, FNP, a medical provider at Integrative Family Medicine of Asheville. You can read more about Katey in her bio.

Vitamin D: Why You Need It and How to Get It Safely