The Essential Guide to Vitamin D: Why You Need It and How to Get Enough

January 01, 2025
MVP Pharmacy

Vitamin D is a crucial nutrient for overall health and well-being. Often called the "sunshine vitamin," it’s produced naturally by your skin when exposed to sunlight. Adequate vitamin D levels are linked to stronger bones, improved mood, better immune function, and potentially lower risks of serious diseases like osteoporosis, cancer, diabetes, and autoimmune conditions.

Yet, vitamin D deficiency is surprisingly common — an estimated 30% to 50% of adults may not be getting enough. Keep reading to learn why vitamin D is essential, who’s at risk of deficiency, the best food sources, and proven ways to optimize your vitamin D levels.

What Is Vitamin D and Why Is It Important?

Vitamin D is unique among nutrients because it acts more like a hormone than a traditional vitamin, influencing a wide range of processes throughout the body.

There are two main forms of vitamin D:

Vitamin D2 (ergocalciferol) – Found in plant-based foods and supplements. This form is less efficiently absorbed by the body.
Vitamin D3 (cholecalciferol) – Produced in the skin when exposed to sunlight and also found in animal-based foods and supplements. Vitamin D3 is the preferred form for supplementation because it is more effective at raising and maintaining vitamin D levels.

Once vitamin D enters your body through sunlight, food, or supplements, it undergoes a two-step conversion process:

First in the liver, it becomes 25-hydroxyvitamin D (25(OH)D) — the circulating form measured in blood tests.
Then in the kidneys, it’s converted to its active form, 1,25-dihydroxyvitamin D, which helps regulate key bodily functions.

Health Benefits of Vitamin D

Vitamin D affects nearly every system in the body through its interaction with vitamin D receptors found in many tissues. Key roles include:

Bone Health: Vitamin D helps the body absorb calcium and deposit it into bones, keeping them strong and healthy.
Immune System Support: It modulates immune responses, reducing inflammation and potentially preventing autoimmune diseases.
Cell Growth Regulation: Active vitamin D plays a role in regulating cell growth, which may lower cancer risk.
Muscle Function: Vitamin D receptors in muscles help maintain muscle strength and coordination. Low levels are linked to muscle weakness and fatigue.

Given these wide-ranging functions, maintaining adequate vitamin D levels is critical for overall health.

Why Is Vitamin D Deficiency So Common?

Despite its importance, vitamin D deficiency is widespread for several reasons:

Aging: Older adults produce less vitamin D from sunlight, and their kidneys convert less to its active form.
Darker Skin Tones: Higher melanin levels reduce the skin’s ability to produce vitamin D from sunlight.
Excess Body Fat: Vitamin D is sequestered in fat cells, making less available for circulation.
Limited Sun Exposure: Modern indoor lifestyles, use of sunscreen, and concerns about skin cancer reduce natural vitamin D production.
Geographic Location: People living in northern latitudes get less UVB exposure, especially in winter months.

With so many factors contributing to low vitamin D levels, many people can't rely on sun exposure alone to meet their needs.

Why Sun Exposure Alone Isn’t Enough

While sunlight is a natural source of vitamin D3, multiple factors limit how much your body can produce:

Time of Day and Season: UVB rays are only available when the sun is high, and less so in winter or at higher latitudes.
Geography and Climate: Cloud cover, pollution, and distance from the equator reduce UVB exposure.
Skin Pigmentation: Darker skin requires longer sun exposure to produce the same amount of vitamin D as lighter skin.
Sunscreen Use: Sunscreens, while essential for preventing skin damage, block UVB rays and hinder vitamin D production.
Aging: Older adults’ skin has fewer compounds needed to synthesize vitamin D.
Body Fat: Vitamin D can become trapped in fat tissue, lowering circulating levels even if intake is adequate.

How Much Sun Do You Need?

Experts suggest 10 to 30 minutes of midday sun exposure on bare skin a few times a week may help — but this varies widely based on skin type, location, and season. Due to these unpredictable factors, supplementation and dietary sources are often necessary to maintain optimal levels.