Can You Be Vitamin D Deficient in the Summer?

Think a vitamin D deficiency is just a “winter you” problem? Think again.

Turns out, low vitamin D levels during the sunnier seasons is surprisingly common as well. This raises questions like: Is there an ideal amount of sun exposure needed? Does sunscreen interfere with this natural process? What about factors like geography, skin tone, age, and time of day?

The answer is yes. These variables all play a role. Vitamin D is often called the “sunshine vitamin,” but getting enough isn’t always as simple as spending more time outdoors. Let’s get into it.

Why Vitamin D Matters

Vitamin D is essential for many functions throughout the body. It helps the body absorb calcium to support strong bones, contributes to normal muscle function, supports communication within the nervous system, and plays an important role in immune health.(🔗)

Vitamin D is unlike most nutrients because it can be produced naturally when ultraviolet B (UVB) rays from sunlight reach the skin. While vitamin D is found in a handful of foods and supplements, this ability to synthesize it from sun exposure has led many people to associate deficiency primarily with the winter months.

The reality, however, is a bit more nuanced.

So if summer brings longer days and more sunshine, why are so many people still deficient? Several factors can influence how much vitamin D your body is actually able to produce and maintain.

Why You Can Still Be Vitamin D Deficient in Summer

1. We Spend More Time Indoors Than We Think

Whether working from home or in an office, commuting, or at the gym, most of our day is spent behind glass. And here’s the important detail: glass blocks UVB rays almost entirely, which means little to no vitamin D production occurs through sun exposure indoors or through windows. 

However, UVA rays still pass through glass in significant amounts. While they do not contribute to vitamin D production, they can contribute to skin damage over time. [🔗]

2. Sunscreen Effectiveness

Sunscreen is primarily designed to reduce UVB exposure, which is the type of UV rays responsible for sunburns. But as previously mentioned, UVB rays are also responsible for vitamin D production in the skin. . An SPF 30 sunscreen can block approximately 95–98% of UVB radiation when applied correctly and in sufficient amounts. Therefore, blocking vitamin D synthesis significantly.[🔗]

However, due to common human error factors like inconsistent application, missed areas, and reapplication timing, a little UVB often squeaks through.

3. Time of Day Matters

Morning dog walks and evening patio dinners may not provide enough UVB exposure for meaningful vitamin D production. During the early morning and late afternoon, the sun sits lower in the sky, which means its rays pass through more of the atmosphere before reaching the skin. This reduces UVB intensity and makes exposure more similar to winter sunlight conditions.

For most locations, UVB rays are strongest between approximately 10 a.m. and 4 p.m., when the sun is higher in the sky.🔗]

4. Skin Tone Matters

Melanin, the pigment that gives skin its color, also helps protect against ultraviolet (UV) radiation. Because of this protective effect, higher levels of melanin can reduce the skin’s ability to produce vitamin D from sunlight. Individuals with darker skin tones may require more sun exposure to produce the same amount of vitamin D as those with lighter skin tones. [🔗]

5. Age Matters

The skin’s ability to produce vitamin D naturally declines with age. Research has shown that older adults can produce significantly less vitamin D from the same amount of sun exposure compared with younger individuals. In one study, adults in their late 70s and early 80s produced less than half the amount of vitamin D as children and teenagers following comparable UVB exposure.

As a result, older adults may be at greater risk of vitamin D deficiency, even during the summer months, and may need to consider additional dietary sources or supplementation to maintain adequate levels.[🔗]

6. Geographic Location Matters

Geography also plays an important role in vitamin D production. The farther a place is from the equator, the more seasonal variation there is in the sun’s angle and the amount of UVB radiation that reaches the Earth’s surface.

Research suggests that above approximately 37° north latitude, the skin’s ability to produce vitamin D from sunlight can become limited during parts of the year outside of summer. Whitefish, Montana sits at roughly 48° north, placing it well within this range of seasonal variability.[🔗]

7. Other Factors That Can Influence Vitamin D Status

Because vitamin D is fat soluble, its absorption depends on the body’s ability to absorb dietary fat. Certain health conditions that affect digestion or fat absorption, such as celiac disease or inflammatory bowel conditions, may contribute to lower vitamin D status.

Signs You Might Need To Check Your Levels

Vitamin D deficiency can present in subtle ways, and symptoms are often non-specific. Common signs associated with low vitamin D levels may include:

• Persistent fatigue
• Muscle aches or weakness
• Frequent illness or slow recovery
• Low mood or seasonal changes in mood
• Bone or back discomfort
• Slow wound healing

These symptoms can have many possible causes, but if several appear together or persist over time, it may be worth discussing vitamin D testing with a healthcare provider.[🔗]

Curious About Your Vitamin D Levels?

If you’re wondering where your vitamin D levels currently stand, testing can offer helpful insight.

We partner with Busy Bee IV Clinic, located just across the street, where vitamin D lab testing is available. Labs must be booked in advance, so call or text to request a vitamin D draw. One advantage of this test is that it does not require fasting, and bloodwork can be completed at any time of day.

Making the Most of Summer Sunlight

As a general rule of thumb, sensible sun exposure can be an excellent source of vitamin D for both children and adults. In this context, “sensible” avoiding exposure lengths that could cause sunburn.

A simple framework often referenced for vitamin D production is:

Sun exposure (without sunscreen): face, arms, hands, and legs
Duration: approximately 5 to 30 minutes
Frequency: about 2 times per week or more
Timing: between 10 a.m. and 4 p.m.

[🔗]

Supporting Your Vitamin D Levels

Vitamin D needs can vary widely depending on sun exposure, geography, skin tone, age, and overall lifestyle. Because of this variability, some people choose to include vitamin D supplementation as part of their daily routine, especially during months or seasons when sun exposure is limited.

Public health guidelines often list a baseline intake range of approximately:

• Infants, children, and adolescents: 400–600 IU per day
• Adults: 600–800 IU per day [🔗]

In practice, supplemental vitamin D is often used in a range of strengths depending on individual needs and consistency of sun exposure.

Within our collection, you’ll find vitamin D products designed for everyday support, including lower-dose options that can easily be incorporated into a daily wellness routine. From customizable drops to convenient gummies for kids & adults alike.

Some of our vitamin D formulations are also paired with vitamin K2, a nutrient often included in supplement routines that focus on bone and mineral support. You can read more about nutrient synergy in our previous blog here.

Symbiosis with the Sun

The sun often gets a bad rap, yet it plays an essential role in human biology, including supporting the body’s natural vitamin D production.

The longer, brighter days of summer can be an opportunity to explore sensible sun exposure, while continuing to balance skin protection, lifestyle factors, and nutritional needs. Together, these elements help support healthy vitamin D levels year-round.