How to Maximize Natural Vitamin D Production

How Latitude Affects Your Vitamin D Levels Throughout The Year

In the summer, the skin can synthesize D3 during a longer period of the day in almost all locations⁴. While in the winter months, in regions of latitudes above 35 degrees, vitamin D synthesis by the skin almost stops^3,4.

In winter, skin exposed to the sun at different latitudes produces varying amounts of pre-vitamin D3. 

• Edmonton, Canada (52°N) – very little D3 is produced in exposed skin from October to March.
• Boston (42°N) – very little D3 is produced in exposed skin from November through February.
• Phoenix, AZ (33.4°N) – the skin is able to produce D3 all year long.
• Los Angeles (34°N) – the skin is able to produce D3 all year long.
• San Juan (18°N) – the skin is able to produce D3 all year long.

How Time Affects Vitamin D Synthesis

In winter, countries above 40° northern latitude don’t receive enough UVB light for the skin to make vitamin D due to a minimum threshold not being met.³.

In terms of the time of the day, the peak production of vitamin D3 occurs around noon, when the zenith angle is smaller, sun rays are more vertical, and the intensity of UVB radiation higher⁴.

How Altitude Affects Vitamin D Synthesis

Altitude matters. The details mentioned earlier are mainly for places at sea level. In higher elevations, where there’s less atmospheric absorption of UVB, vitamin D synthesis can still occur on sunny winter days.⁴.

The Impact of Weather and Pollution on Vitamin D from Sunlight

According to the Smithsonian Environmental Research Center, “increases in cloud cover, pollution, dust, smoke from wildfires and other airborne and waterborne particles related to climate change decrease UV light penetration⁶.”

Polluted air, with things like nitrous oxide and sulfur dioxide, soaks up solar UVB radiation. This lowers the skin’s vitamin D3 production during sun exposure. In cities with high pollution, like Los Angeles and San Diego, living at lower latitudes might not bring as much sun-related benefits. ⁷.

Studies support the idea that pollutants in the air can decrease UVB intensity at the Earth’s surface. This contributes to less vitamin D synthesis in the skin and lower vitamin D levels, especially in populations living in highly polluted areas.⁸

Why Glass and Plastic Can Prevent Vitamin D Absorption

Glass and plastic filter radiation, decreasing exposure to sunlight, especially the UVB band. This might prevent the body from producing vitamin D.

How Lifestyle Choices Influence Vitamin D Production

To get sufficient vitamin D from sunlight, it’s important to spend time in the sun with enough exposed skin. Your personal choices matter, as even during summer with plenty of sunlight, three factors can hinder vitamin D3 production:

• avoiding the sun or staying in the shade
• wearing clothes
• using sunscreen

Clothing and Vitamin D Deficiency: What You Need to Know

A study checked fabrics like cotton, wool, and polyester in black and white. It found that none of these fabrics let your skin make vitamin D3 or increase vitamin D3 in your blood when you’re in the sun. Researchers concluded that clothing prevents or significantly impairs UVB radiation-dependent formation of vitamin D3¹⁰.

As pointed out by the authors of the study Vitamin D: Production, Metabolism and Mechanisms of Action, clothing “is one likely explanation for the observation that the Bedouins in the Middle East, who completely cover their bodies with clothing, are more prone to develop rickets and osteomalacia than the Israeli Jews with comparable sunlight exposure⁴.”

Vitamin D deficiency is a global issue. Many countries in the Middle East and Asia have low vitamin D levels, despite having lots of sunlight. This is often because of human behavior, like avoiding the sun and wearing clothes, which greatly affects vitamin D levels.

Different parts of the world have varying levels of vitamin D, mainly because of cultural, educational, and religious factors influencing sun exposure. For instance, in Europe, less than 20% of the population in Northern Europe has vitamin D deficiency, while 30-60% in Western, Southern, and Eastern Europe do. In the Middle East, up to 80% of the population may have vitamin D deficiency.¹².

Surprisingly, areas with more sunlight often have more vitamin D deficiency. North America, for example, has the highest vitamin D levels, despite being known for having a lot of sunlight.¹¹.

Sunscreen Use and Its Effect on Vitamin D Levels

The use of sunscreen is complex as it is widespread without sufficient information about potential risks. While many associate sun exposure with skin issues such as cancer, most are unaware that certain sunscreen ingredients may be harmful and impact hormones¹³.

Sunscreens have several benefits: they block the cutaneous absorption of UVB radiation and prevent sunburning, premature aging, and skin cancer. However, studies also found that sunscreens may inhibit or completely block vitamin D production, especially under controlled conditions^14,15,16,17.

Some researchers are saying that what they found in the lab might not be the same as what happens outside in the sun. They mention that using artificial UV radiation in studies, which is different from natural sunlight, has a big impact and doesn’t show what happens in the environment.”

Does Sunscreen Block Vitamin D Production?

In a study demonstrating that sunscreens block skin vitamin D synthesis, the authors observed a small impact on circulating 25(OH)D. This might be due to a shift to another internal source of precursors.¹⁴.”

The thickness of the sunscreen layer, controlled in research studies, is also a major factor in the sunscreens ability to block vitamin D production¹⁵, which may explain why “real life” results may differ from controlled studies.

Controlled field studies also exist, but often with “real life” limitations. Some of these studies ignore the most important factors that influence the results, namely personal UV radiation exposure, sunscreen application thickness and body surface area exposed¹.

How UVA and UVB Protection Influence Vitamin D Synthesis

SPF (sun protection factor) refers to sunscreen protection against UVB radiation. But what if UVA protection was more important?

A 2019 study found that “optimal sunscreen use, during a sun holiday with a very high ultraviolet index, allows vitamin D synthesis without sunburn.” This study concluded that “sunscreens (sun protection factor, SPF 15) applied at sufficient thickness to inhibit sunburn during a week-long holiday with a very high UV index still allow a highly significant improvement of serum 25-hydroxyvitamin D3 concentration.” Adding that an “SPF 15 formulation with high UVA protection enables better vitamin D synthesis than a low UVA protection product. The former allows more UVB transmission¹⁹.”

What the Research Says About Sunscreens and Vitamin D

The amount of UVA protection, which the current SPF value doesn’t show, is a key factor emphasized in recent publications. This includes a review by a group of international experts.¹. The authors of different articles refer that:

• “A high UVA-PF sunscreen enables significantly higher vitamin D synthesis than a low UVA-PF sunscreen because the former, by default, transmits more UVB than the latter¹⁹.”
• “Daily sunscreen use, for nonintentional solar exposure, is mainly based on products with low SPF and high UVA‐PF. This is unlikely to impact on vitamin D production¹.”
• “When tested outdoors, sunscreens with a given SPF, especially with high UVA protection, were less likely to block vitamin D production than when tested in the laboratory²⁰.”

Unfortunately, although there are broad-spectrum sunscreens that block both UVA and UVB, there is currently no standard for listing UVA-blocking power.

Sunscreen “Discordance”

The conclusions from diverse studies are many, diversified, and often contradictory. The authors of a 2019 review on “The effect of sunscreen on vitamin D” probably hit the target when highlighting the lack of adequate evidence: “While the experimental studies support the theoretical risk that sunscreen use may affect vitamin D, the weight of evidence from field trials and observational studies suggests that the risk is low. We highlight the lack of adequate evidence regarding use of the very high sun protection factor sunscreens that are now recommended and widely used¹⁸.”

What the Research Says About Sunscreens and Vitamin D

Sunscreens, especially those with strong UVA protection, might or might not affect making vitamin D in everyday situations. It depends on factors, mostly how people behave. But, for sure, many sunscreens have ingredients that could be harmful. When you think about using sunscreen, it’s crucial to know all the ingredients and the possible risks.

We have an excellent blog “Do Sunscreens Contribute to Vitamin D Deficiency?” where we have discussed the use of different sunscreens, their benefits and risks, and we highly recommend that you click on the link and read it.

Skin Color and Vitamin D: How Melanin Affects Synthesis

As we mentioned before, people with darker skin have “natural sun protection” because they have more melanin. Melanin in the skin absorbs UV rays, kind of like a shield, competing with the process that makes vitamin D3. This can make sunlight less effective in producing D3 in the skin. ²¹.

People with darker skin, usually more exposed to sunlight, produce less vitamin D3 because they have more melanin4. This means they need to be exposed three to five times longer than lighter-colored skin people to achieve similar vitamin D levels²².

Vitamin D and Age: Why Older Adults Are More at Risk

Older people have low vitamin D levels, often due to not eating enough foods with vitamin D and getting less sunlight. Studies found that aging can cut the skin’s ability to make pre-vitamin D more than twice as much.

Some of the processes by which aging affects the formation of the active form of vitamin D (calcitriol), include²⁵:

• Decreased calcium absorption.
• Intestinal resistance of calcium absorption to circulating calcitriol.
• Decreased VDR (vitamin D receptors).
• Decreased renal production of calcitriol by the aging kidney.
• Decreased skin production of vitamin D.
• Substrate deficiency of vitamin D.

Vitamin D deficiency or inadequacy puts the elderly population at elevated risk of muscle fiber atrophy, chronic musculoskeletal pain, sarcopenia, and falls and fractures^23,26.

Sex Differences and the Effects of Vitamin D on Hormones

A systematic review of the literature, using 195 studies conducted in forty-four countries involving more than 168,000 participants reported that “sex-related differences were not observed in any region¹¹.” Nonetheless, vitamin D seems to exert some beneficial effects against autoimmune conditions, for example by acting in synergy with estrogens²⁷. Therefore, gender can be an important variable when evaluating the potential power of vitamin D on certain conditions, such as autoimmune diseases and cancer^27,28.

Health Conditions That Increase Risk for Vitamin D Deficiency

Certain health conditions make people more sensitive to sunlight, and they need extra protection. This puts them at a higher risk of vitamin D deficiency. This is true for people with genetic or acquired photosensitivity disorders who need careful protection from sunlight.¹.

People who had skin cancer or organ transplants are more likely to lack vitamin D. Experts say they should use strong sunscreen, wear protective clothes, and stay in the shade. They also suggest taking vitamin D supplements and getting regular checkups. They also recommend taking vitamin D supplements and getting screened regularly.^1.

Obesity and Malabsorption: Barriers to Getting Enough Vitamin D

Obesity has also been associated with vitamin D deficiency^29,30. As explained in the literature insufficiency “is likely due to the decreased bioavailability of vitamin D3 from cutaneous and dietary sources because of its deposition in body fat compartments²⁹.” Men and women with a BMI greater than 30 require at least 2 to 5-fold increase in their vitamin D requirement³⁰.

People with conditions like Crohn’s disease, ulcerative colitis, cystic fibrosis, and those who’ve had gastric bypass surgery are at a higher risk of vitamin D deficiency because their bodies don’t absorb it well. They may need larger vitamin D doses to meet their needs. Celiac disease, which affects how the intestine absorbs nutrients, can also silently cause vitamin D deficiency. Sometimes, this disease is only discovered when a person with low vitamin D levels doesn’t respond well to vitamin D treatment, revealing an absorption issue.³⁰.”

Nutrition and Dietary Sources of Vitamin D: What Works and What Doesn’t

Food has very little vitamin D, and getting enough from what you eat, even if it’s fortified, can be hard. Inuit and some indigenous groups might be an exception because they eat vitamin D-rich foods like oily fish, seal and whale blubber, and polar bear liver.⁷.

Comparing vitamin D produced in the skin and ingested in the diet:

• Vitamin D synthesized in the skin – 100% of it is potentially bound to the vitamin D binding protein⁷.
• Vitamin D ingested from the diet or dietary supplements – approximately 60% is bound to the vitamin D binding protein and 40% is cleared in the lipoprotein bound fraction⁷.

Although most of the body’s vitamin D demand is met by sunlight, and only a small percentage is obtained from food, implementing vitamin D-rich foods in the diet can always contribute to prevent insufficiency and deficiency.

High-Risk Groups for Vitamin D Deficiency: Who Should Be Concerned?

Depending on several variables, both personal and cultural, some groups seem to be more at risk of vitamin D deficiency^1,11,12:

• Newborns
• Young children
• Adolescents
• Pregnant women
• Elderly (especially when institutionalized)
• Institutionalized people
• People wearing clothing that covers most of the body
• Deeply pigmented skin (darker skin)

IMPORTANT: Increased skin pigmentation, changes in latitude, seasonal changes, time of day, sunscreen use, and aging, among other factors, significantly affect the cutaneous production of this vitamin D.

People with more melanin (darker skin) need more sun exposure when compared with those who have less melanin. This is aggravated when those people live in the Northern Hemisphere, making the probability of Vitamin D deficiency very high.

Should You Avoid the Sun? Balancing Sun Protection and Vitamin D Needs

Unfortunately, with more people spending time indoors due to work, digital activities, and home comforts, there’s also a rise in behaviors like avoiding the sun and using sun protection. The push to prevent skin cancer through campaigns has made people more inclined to limit their time in the sun^.31.

This fact is well described by an article published in the International Journal of Environmental Research and Public Health:

“While it is accepted that solar UVR exposure is the main cause of skin cancer, evidence is accumulating on the health benefits of sun exposure, as well as widespread vitamin D deficiency, and has revealed a possibly significant public health problem resulting from insufficient sun exposure. This suggests that current public health advice on sun exposure ought to be reconsidered to communicate a better balance of the benefits and harms of sunlight, particularly at higher latitudes where ambient levels of UVR are comparatively low even in summer³¹.”

Chronic excessive exposure to sunlight does increase the risk of nonmelanoma skin cancer. However, avoiding all direct sun exposure, clothing and sunscreen use increases the risk of vitamin D deficiency exponentially. We have already discussed the many health consequences of vitamin D deficiency/ insufficiency. 

Restore Balance Naturally at An Oasis of Healing: The Vital Role of Vitamin D in Your Wellness Journey

Vitamin D plays an essential role in your body’s immune function, bone health, hormonal balance, and even cancer prevention. At An Oasis of Healing, we understand that optimal healing requires a whole-body approach—one that integrates sunlight, nutrition, detoxification, and personalized care. Many people unknowingly suffer from vitamin D deficiency due to modern lifestyles that limit sun exposure, poor dietary intake, and chronic health conditions. 

At An Oasis of Healing, we incorporate natural methods of vitamin D optimization, including safe sun exposure, therapeutic nutrition, and supplementation, as part of our comprehensive integrative cancer treatment protocols. If you’re looking to restore health at the root level, we invite you to learn more about becoming a patient.

References

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