What months of the year should you take vitamin D? A Nutrition Diet Guide

October 9, 2025 •

3 min read

According to the National Institutes of Health (NIH), an estimated 1 billion people worldwide suffer from vitamin D deficiency, a number that increases significantly during the colder months in northern latitudes. A key component of a balanced nutrition diet, knowing what months of the year should you take vitamin D is crucial for maintaining optimal health, especially for bone density and immune function.

Quick Summary

Vitamin D supplementation is crucial during autumn and winter, from roughly October to March, when sunlight is insufficient for natural production. Factors like latitude, skin tone, and lifestyle affect individual needs. Some people require year-round supplementation to maintain adequate levels, making dietary sources and smart sun exposure important considerations.

Key Points

Winter Supplementation: The months from roughly October to March are when most people in northern latitudes should consider taking a daily vitamin D supplement due to insufficient sunlight.
Year-Round Needs: High-risk groups, such as older adults, people with darker skin, and those with limited sun exposure, should consider taking vitamin D supplements throughout the entire year.
Seasonal Sunlight: Between April and September, most people can get adequate vitamin D from short, regular periods of midday sun exposure, but this should be done safely to avoid skin damage.
Dietary Support: While few foods are naturally rich in vitamin D, fortified foods like milk and cereals, along with fatty fish, are important dietary sources, especially during winter.
Know Your Risk: Factors like age, skin tone, geographic location, and medical conditions significantly impact vitamin D synthesis and absorption, necessitating a personalized approach to supplementation.
Safe Intake: Consulting with a healthcare professional is important to determine appropriate vitamin D intake and avoid potential health issues from excessive consumption.

Why Seasonality Matters for Vitamin D Production

Vitamin D is often called the "sunshine vitamin" because our skin produces it when exposed to sunlight. Specifically, ultraviolet-B (UVB) rays from the sun interact with a compound in our skin to synthesize vitamin D3. However, this process is highly dependent on a number of factors, most importantly the season and geographic location. The angle of the sun changes throughout the year, meaning that in higher latitudes, the UVB rays are too weak during autumn and winter to stimulate sufficient vitamin D production.

In regions like the UK, the period between October and early March is considered the "vitamin D winter," when sun-induced synthesis is minimal. Northern areas like Edmonton, Canada, may have an even longer period of insufficient sun exposure. Conversely, those living closer to the equator can produce vitamin D from sunlight year-round. Understanding this seasonal variation explains why supplementation is recommended during the colder, darker months.

The Role of Vitamin D Beyond Seasonal Changes

Beyond seasonal requirements, several groups are at a higher risk of vitamin D deficiency and may need to supplement throughout the entire year, regardless of sun exposure. Consulting a healthcare provider for a blood test can help determine individual needs.

Older Adults: Skin's ability to synthesize vitamin D decreases with age.
Individuals with Darker Skin: Melanin reduces UVB absorption, requiring more sun exposure for production.
People with Limited Sun Exposure: This includes those who are housebound, live in care, or spend long hours indoors.
Those with Malabsorption Issues: Conditions like Crohn's disease or obesity can impair vitamin D absorption from food.
Infants and Young Children: Breastfed infants often need supplementation.

Comparison of Vitamin D Sources by Season


Source	Spring/Summer (April-September)	Autumn/Winter (October-March)
Sunlight	Primary source for most in temperate climates; short midday exposure is often sufficient.	Insufficient for adequate synthesis in higher latitudes.
Diet	Valuable supplementary source, but often not sufficient alone. Fortified foods and oily fish are helpful.	Crucial for obtaining vitamin D when sun is limited. Focus on fortified products and fatty fish.
Supplements	Not always necessary for the general population with sufficient sun exposure. Useful for at-risk groups.	Highly recommended and often necessary for almost everyone in northern latitudes.

Optimizing Your Vitamin D Intake for Health

A comprehensive approach using diet, sunlight, and supplementation is most effective for maintaining healthy vitamin D levels year-round. Safe sun exposure during summer is beneficial, while supplements offer consistent intake.

Dietary Considerations

Dietary sources contribute to vitamin D intake. Good options include:

Fatty Fish: Excellent natural source like salmon and mackerel.
Fortified Foods: Milk, cereals, and plant-based alternatives are often fortified.
Mushrooms: Some UV-treated mushrooms provide vitamin D2.
Egg Yolks and Red Meat: Contain small amounts.

Supplementation Guidance

Supplementation is widely recommended during autumn and winter by health bodies.

At-Risk Groups: Advised to supplement year-round.
Precautions: Excessive intake can lead to hypercalcaemia. Consult with a healthcare professional regarding appropriate limits.

Sunlight Exposure

During sunnier months, aim for short periods of midday unprotected sun exposure on skin. Always use sun protection for longer durations to minimize skin cancer risk.

Conclusion

Understanding the seasonal impact on vitamin D production is crucial for a healthy nutrition diet. While summer sunlight is a good source for many, autumn and winter in higher latitudes increase deficiency risk. Supplements are vital during this period for many, and year-round supplementation is the safest for specific populations at higher risk. A personalized approach based on your location, lifestyle, and health needs ensures optimal vitamin D levels throughout the year.

Consult a healthcare professional or registered dietitian for personalized guidance based on blood tests and lifestyle factors.

National Institutes of Health Office of Dietary Supplements Vitamin D Fact Sheet

Frequently Asked Questions

No, your body has a built-in mechanism that prevents it from overproducing vitamin D from sun exposure alone. The risk comes from excessive supplementation, not from sunlight. However, prolonged sun exposure increases the risk of skin damage and skin cancer.

A blood test measuring your 25-hydroxyvitamin D levels is the most accurate way to determine your vitamin D status. While general guidelines exist, a blood test provides a personalized assessment and helps your doctor recommend if supplementation is needed.

Yes, people with darker skin have more melanin, which acts as a natural sunscreen and reduces the skin's ability to produce vitamin D from sunlight. They often require more sun exposure or year-round supplementation to maintain adequate levels.

For most people, it is very difficult to get enough vitamin D from food sources alone, especially during the darker months. While a healthy diet with fortified foods and oily fish helps, supplementation is often necessary, particularly in winter.

General recommendations for vitamin D intake can vary based on age, location, and health status. Many public health bodies suggest considering a supplement during periods of limited sun exposure, such as autumn and winter. It is best to consult with a healthcare professional for personalized guidance.

Both vitamin D3 (cholecalciferol) and D2 (ergocalciferol) can raise blood levels of vitamin D. However, many experts and studies suggest that D3 is more effective at correcting deficiency because it is slightly more active in the body. D3 is naturally produced by animals (including humans), while D2 is the plant form.

Severe vitamin D deficiency can lead to serious bone health issues. In children, it can cause rickets, while in adults, it can lead to osteomalacia (soft bones), causing bone pain and weakness. It can also increase the risk of bone fractures.