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Think you’re getting enough vitamin D from the sun?


Blazing hot summer sun boosts vitamin D

“I’m getting my Vitamin D,” said the woman baking in the sun. Is she? Maybe, maybe not. Sunshine probably isn’t enough for us to get the amount of Vitamin D throughout the year we need to maintain our health, especially as we age. There are ways, however, to ensure that we receive our Vitamin D benefits from the time we do spend in the sun.

A National Health and Nutrition Examination survey reported that more than 40% of adult participants (aged 20 years and older) were Vitamin D deficient, with the numbers even higher among women and seniors. As women over 60, we need to understand why relying solely on sunshine for our Vitamin D needs is simply not enough. Let’s look at the science.

Why Vitamin D matters

Vitamin D is more than strong bones, though that’s certainly important at our age. But this vitamin is a powerhouse nutrient that supports our immune system, helps maintain muscle strength, and may even play a role in preventing certain cancers and heart disease.

Powerhouse indeed.

You might be wondering, “Can’t I just get my Vitamin D from the sun?” Unfortunately, it’s not that simple, and here’s why. Our bodies can produce Vitamin D when our skin is exposed to sunlight. But the process is complex and becomes less efficient as we age.

How much Vitamin D do we need at our age?

The National Academy of Medicine has placed the recommended dietary allowance, or RDA, for Vitamin D at 800 IU (international units) per day for adults older than 70. Between 5 and 30 minutes of sun exposure to unprotected skin (face, arms, legs, or back) between 10 AM and 3 PM, two to three times per week, is generally sufficient for most people to produce adequate Vitamin D to maintain health.

Sun + Skin = Vitamin D. How does it work?

UVB rays—and only UVB rays—catalyze the production of Vitamin D. When UVB rays from the sun hit our skin, they interact with a form of cholesterol in our skin cells. This triggers a series of reactions that eventually lead to the production of Vitamin D. The vitamin then travels through our bloodstream, is processed by our liver, and then is finally activated by our kidneys. It’s an intricate process and, unfortunately, it doesn’t work as well in our older years.

UVB vs UVA rays

Unfortunately, UVB rays are reflected and blocked by the atmosphere, so they are diminished by the time they reach the surface of the earth. Clouds, ozone, and pollution also block UVB rays, as does glass (e.g., windows), sunscreen, and clothing. If it’s cloudy or overcast, you probably aren’t going to produce any Vitamin D. UVB rays must strike your exposed skin to make Vitamin D creation possible.

On the other hand, UVA rays pass relatively unfiltered through the atmosphere, so regardless of the angle of the sun or cloud cover, a high percentage of UVA rays are still reaching the surface of the earth. But UVA rays don’t produce Vitamin D.

Why don’t we get enough Vitamin D from the sun?

As older women our minimum RDA of Vitamin D is 800 IU. But as we age, our skin gets thinner and contains less of the cholesterol needed to start this process. But there are other factors.

  1. The angle of the sun

The angle of the sun significantly affects Vitamin D production in the skin.

It may not have occurred to you, but the angle at which rays of sunlight touch your skin determines whether your body is producing Vitamin D. The sun needs to be between 35 and 50 degrees above the horizon for Vitamin D production to occur.

Sun position at 35° and 50° angles

Angle of the sun necessaryfor skin to produce Vitamin D

Here’s an illustration showing the sun at 35 and 50 degrees high in the sky. The sun’s positions are represented by yellow circles, with dashed lines indicating the angles from the ground. This can help you visualize how the sun’s position changes at different angles.

  1. Time of day

Vitamin D production is most efficient when the sun is highest in the sky, typically between 10 AM and 3 PM.

The sun’s UVB rays are most intense at noon when it’s at its highest point, making this the most efficient time for Vitamin D production. This is also when the sun most damages skin, so the quest for Vitamin D must be balanced with protection against skin cancer and premature aging of skin.

Sun angles on skin between 11 a.m. and 3 p.m. in New York City in June

Angle of the sun between 11 am and 3 pm in June

This image shows the angles of the sun on skin between 11 a.m. and 3 p.m. during June in New York City. The dashed lines indicate the angles from the ground (65°, 70°, and 73°). This visualization helps to understand how the sun’s position varies during these peak hours.

  1. Length of exposure and doses

For most people, between 5 and 30 minutes of sun exposure to unprotected skin (face, arms, legs, or back) between 10 AM and 3 PM, 2 to 3 times per week, is typically sufficient for adequate Vitamin D production. However, much of this depends on where you are and how much skin is exposed.

In case you were wondering whether you can double or triple the time to make even more Vitamin D, the answer is no.

The body stops producing Vitamin D after a certain period of sun exposure due to a self-regulating mechanism that prevents excessive production.

The body reaches its maximum Vitamin D production quickly. This typically occurs within about 15 to 30 minutes of midday sun exposure for most people with fair skin.

After reaching this limit, the body stops producing more Vitamin D to prevent toxicity. This means that continued sun exposure beyond this point does not increase Vitamin D levels but can increase the risk of skin damage.

  1. Location, location, location

The necessary amount of time in the sun for Vitamin D production varies significantly with latitude and altitude.

In a study conducted in three regions of France—an urban area in the flat North, the southern French Southern Alps, and Réunion Island in the Indian Ocean—researchers found the time required for Vitamin D synthesis on the mainland sites was relatively long. Even around solar noon, in winter months this could be 2 to 3 hours for individuals exposing their face and hands.

In the tropics Vitamin D could always be synthesized in a reasonable time (e.g., 20 minutes in winter). By contrast, in summer, the required duration times (exposing face, hands, arms and legs) are very short, approximately 2-4 minutes on the mainland and one minute in the tropics.

  1. Amount of skin exposed

About 25% of your body surface area should be exposed to sunlight. This typically includes the face, arms, legs, or back.

What does 25% of a body’s skin surface look like? One example is the entire chest and abdomen (18%) plus one full arm (9%). Or the entire back and buttocks (18%) plus half of one leg (9%); each leg represents 18% of total body surface area.

Of course, neither of these represents the way most people dress (or undress) outside. But it should give you an idea of how much of your skin, and where it’s located on your body, you need to expose to the sun.

  1. Seasonal variations

Seasonal variations play a role in Vitamin D production. In an article published by UCLA Health, Dr. Robert Ashley, MD, found that in the summer in Miami — with 25 percent of the body exposed to the sun — a person would need only three minutes of sun exposure to make a sufficient amount of Vitamin D.

That same person — when placed in Boston in the winter — would need nearly two hours of sun exposure, at noon, to produce enough Vitamin D because of both the angle of the sun and the likelihood that only 10 percent of the body is exposed.

Vitamin D deficiency tends to be higher during winter months. This is particularly relevant for seniors living in northern latitudes with shorter days and weaker sunlight.

Angles of the sun in New York City change with the seasons

Angle of sun in June and December

This illustration shows how the angles of the sun on skin between 11 a.m. and 3 p.m. change with the seasons.

How to ensure you are getting enough Vitamin D

If you follow the guidelines above you will be able to get your daily dose of Vitamin D from the sun, at least in the warm months. But when the days are short and the temperature drops, the sun may not be your most reliable source. That’s when you should…

  • Talk to your doctor about your Vitamin D levels and ways to achieve your optimal daily dose. Testing usually isn’t necessary unless you are seriously deficient. Also, many medications common in our age group can interfere with the vitamin’s production or absorption.
  • Incorporate Vitamin D-rich foods into your diet: fatty fish, egg yolks, and fortified dairy products.
  • Consider a Vitamin D supplement but consult with your doctor first. They can evaluate your current levels and recommend the right dosage for you.
  • If you live in an area with limited sunlight, talk to your doctor about using a Vitamin D lamp or light box.

Even if we can’t rely on sunshine alone for our Vitamin D needs, we have options. By understanding the challenges we face and taking proactive steps, we can ensure we’re getting the Vitamin D our bodies need. This isn’t about fearing the aging process. It’s about embracing it with knowledge and taking control of our health.

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