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Vitamin D: Benefits, Sources, and Daily Essentials

Discover the power of vitamin D, its essential health benefits, the best natural resources, and expert tips to maximize absorption.
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Vitamin D
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When people talk about “the sunshine vitamin,” they’re referring to vitamin D. Unlike most nutrients, your body can actually produce it when your skin is exposed to sunlight. Still, many people worldwide struggle with low levels. This deficiency is linked to fatigue, bone weakness, and even a greater risk of chronic disease.

So why does vitamin D matter so much, how do you get enough of it, and should you consider supplements? Let’s walk through the basics.

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that functions like a hormone in the body. Once absorbed, it’s converted into its active form, calcitriol, which regulates calcium and phosphorus—two minerals essential for strong bones and teeth.

Interestingly, vitamin D plays a role far beyond bone health. It influences immune function, muscle strength, and even mood regulation. Because of this, it has become one of the most studied nutrients in modern nutrition.

Forms of Vitamin D

There are two main forms you’ll see on food labels and supplements:

  • Vitamin D2 (ergocalciferol): Found in some plants and fortified foods. It’s less potent and shorter-lasting in the body.
  • Vitamin D3 (cholecalciferol): Produced in your skin from sunlight and found in animal-based foods. D3 is more effective at raising and maintaining blood levels.


Most experts agree that vitamin D3 is the preferred form for supplementation.

Health Benefits of Vitamin D

Supports Bone Health

Vitamin D helps your body absorb calcium and phosphorus from food. Without it, bones can become brittle and weak, increasing the risk of osteoporosis and fractures. According to the NIH, vitamin D deficiency in children leads to rickets, while in adults it contributes to osteomalacia [1].

Strengthens the Immune System

Your immune cells use vitamin D receptors to help fight infections. Studies in the British Medical Journal (2017) suggest vitamin D supplementation can reduce the risk of respiratory infections, especially in people with low baseline levels [2].

Improves Muscle Function

Vitamin D plays a role in muscle strength, which may help prevent falls in older adults. Research also suggests it may support recovery and reduce muscle weakness in deficiency states [3].

May Support Mood and Brain Health

Some studies link low levels to depression and cognitive decline. While research is ongoing, ensuring adequate levels may support emotional well-being [4].

Potential Role in Chronic Disease Prevention

Emerging evidence connects this vitamin with reduced risk of certain chronic conditions, including heart disease and type 2 diabetes. Although results are mixed, maintaining healthy levels is considered an important piece of overall wellness [5].

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Food Sources of Vitamin D

Unlike many vitamins, vitamin D is not found in large amounts in most foods. Here are some of the best dietary sources:

  • Fatty fish: Salmon, mackerel, sardines, and tuna
  • Egg yolks
  • Fortified foods: Milk, orange juice, cereals, and plant-based milks
  • Cod liver oil: A concentrated traditional source


Still, it’s tough to reach daily needs from diet alone, which is why sunlight and supplements often come into play.

Quick Food Chart: Vitamin D Sources

Food

Serving Size

Approx. Vitamin D (IU)

Salmon (cooked)

3 oz

450–600 IU

Mackerel (cooked)

3 oz

350 IU

Sardines (canned)

2 fish

45 IU

Egg yolk

1 large

40 IU

Fortified milk

1 cup

100 IU

Fortified cereal

1 serving

40–100 IU

How Much Do You Need Daily?

Recommended Daily Intake

According to the National Institutes of Health (NIH), the recommended daily intake for vitamin D is:

  • Infants (0–12 months): 400 IU (International Units)

  • Children (1–18 years): 600 IU

  • Adults up to 70 years: 600 IU

  • Adults over 70 years: 800 IU

  • Pregnant and breastfeeding women: 600 IU

Some experts suggest that higher daily amounts—up to 1,000–2,000 IU—may be beneficial for adults to maintain optimal blood levels, especially if sun exposure is limited. It’s always wise to have your vitamin D levels tested and discuss your ideal intake with a healthcare provider before starting supplementation.

👉 Fun Fact: Blood levels are usually measured by testing serum 25-hydroxyvitamin D.

A healthy blood level is generally considered between 30–50 ng/mL, but some practitioners aim for slightly higher depending on individual needs.

Sunlight and Vitamin D

Exposure to sunlight is one of the easiest ways to boost vitamin D levels. When UVB rays hit your skin, they trigger vitamin D3 production.

However, several factors affect how much vitamin D you can make:

  • Geography: People living farther from the equator produce less, especially in winter.
  • Skin tone: Darker skin produces less vitamin D from the same sun exposure.
  • Sunscreen use: Sunscreen blocks UVB, reducing production (though it’s still important for skin cancer prevention).


Because of these variables, even people who spend time outside may still fall short.

Signs of Deficiency

Deficiency is common worldwide and can show up in subtle ways, including:

  • Frequent illness or infections
  • Fatigue or low energy
  • Bone or back pain
  • Muscle weakness
  • Mood changes


If you suspect deficiency, a blood test from your doctor is the only way to confirm your levels.

Conclusion

From supporting strong bones to boosting immunity, vitamin D is essential for overall health. Yet, many people don’t get enough from diet or sunlight alone. By focusing on food sources, smart sun exposure, and quality supplements when needed, you can make sure your levels stay in a healthy range.

If you’re not getting enough from diet and sunlight, don’t worry—we’ve got you covered. Check out our guide, “Vitamin D3 and K2: Benefits and How They Work Together.” It includes our top pick D3 and K2 supplements. 

Last Updated: August 27, 2025

Disclaimer: This content is for informational purposes only and should not be considered medical advice. Always consult a qualified healthcare provider before making dietary changes.

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About the Author

Jalaine McCaskill, founder of Tweaksly, offers practical, research-based nutrition tips and reviews to make healthy eating simple and achievable.

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References:

  1. Kaur J, Khare S, Sizar O, et al. Vitamin D Deficiency. [Updated 2025 Feb 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532266/

  2. Martineau, A., et al. (2017). Vitamin D Supplementation to Prevent Acute Respiratory Tract Infections: Systematic Review and Meta-Analysis of Individual Participant Date. BMJ, 356. DOI: https://doi.org/10.1136/bmj.i6583

  3. Sultan, S., Taimuri, U., Basnan, S. A., Ai-Orabi, W. K., Awadallah, A., Almowald, F., & Hazazi, A. (2020). Low Vitamin D and Its Association with Cognitive Impairment and Dementia. Journal of aging research, 2020, 6097820. https://doi.org/10.1155/2020/6097820

  4. Álvarez-Mercado, A. I., Mesa, M. D., & Gil, Á. (2023). Vitamin D: Role in chronic and acute diseases. Encyclopedia of Human Nutrition, 535–544. https://doi.org/10.1016/B978-0-12-821848-8.00101-3

  5. Gunton, J. E., & Girgis, C. M. (2018). Vitamin D and muscle. Bone reports, 8, 163–167. https://doi.org/10.1016/j.bonr.2018.04.004