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Time It Takes For Vitamin D Levels To Drop After Prolonged Sun Exposure in Summer

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Your body can store Vitamin D for a period of time before you become deficient, find out more below.

How Quickly Will Vitamin D Levels Drop After the Summer?

Often referred to as the “Sunshine vitamin,” vitamin D can be best utilized by your body when it is metabolized by direct exposure to sunlight. While the family of D vitamins ranges from D1 to D5, the most important for you metabolically are D2(ergocalciferol) and D3 (cholecalciferol).

Vitamin D is integral for many physiological functions, including calcium absorption and bone health. A deficiency in vitamin D can put you at risk for bone diseases, compromised heart and nerve functioning, mental confusion, and even kidney damage.

In light of these health concerns, many people wonder how long their vitamin D reserves will last into the winter. Will a summer of sunbathing sessions give you enough vitamin D to stay healthy until springtime? Understanding the factors that affect how vitamin D is stored in your system will answer this question.

What Affects Your Vitamin D Levels?

The best way to boost your vitamin D levels is through sunlight. According to Harvard Health, your body can produce as much as 20,000 IU of vitamin D3 during thirty minutes of whole-body sun exposure, depending on the strength of the light in question. Numerous factors affect its metabolism, including the following:

Geographic Location: Sunlight with a UV index strong enough to generate vitamin D is a daily occurrence in the tropics, but it's only possible in the late spring, summer and early fall months in temperate regions, and even less common closer to the poles(above 37 degrees north latitude and below 37 degrees south).

The angle of the Sun's Ray: The angle that sunlight penetrates the atmosphere affects its vitamin D production potential. Low angle light naturally means that most UVB light is blocked, consequently lowering UVB production. This includes both early and late in the day, as well as during the late fall, winter, and early spring seasons. The general rule is that casting a shadow longer than you are tall means that the sun's angle is too low for meaningful vitamin D production.

Skin Type: Your skin type dictates the amount of sunlight exposure required for vitamin D production. Darker skin contains more eumelanin, which means that it better protects against skin damage than lighter skin. However, the same skin pigment that shields skin from harm also stops its melanocytes from absorbing as much sunlight for vitamin D production.

This makes a significant difference in overall absorption levels. Research from the University of Pennsylvania found that light-skinned participants could experience as much as a 50-fold increase in their blood's vitamin D levels within eight hours of exposure to sunlight, while it took darker skinned participants over 40 hours to achieve a 30-fold increase in their amounts.

Age: The young and old alike are less efficient at generating vitamin D from sunlight. People older than age sixty and younger than 20 need more prolonged sun exposure to produce adequate amounts of vitamin D because their skin has lower levels of 7-dehydrocholesterol than younger adults.

Time Spent Indoors: Though sunlight itself can pass through glass, the panes block most of the UVB spectrum light. This means that indoor workers are often deficient in vitamin D, even if they spend their days near sunny windows.

Unlike water-soluble vitamins that your body regularly excretes out in urine, vitamin D can be stored in fatty tissue. This means sufficient vitamin D production during part of the year can bank up your levels for when options for sunlight become slim.

How long will your vitamin D levels last? That question has caused considerable debate.

How Long Will Vitamin D Last in Your Body?

Because the previously listed factors affect vitamin D metabolization and any excess amounts are stored in fatty tissue, it's difficult to make broad statements about how long a seasonal dose will last in the body.

Generally speaking, healthy people store roughly a three-month supply of vitamin D within their bodies during the summer months.

To determine how long a compound stays within your body, doctors look at its half-life, or the length of time it takes for half of it to be removed from the body. The half-life of calcidiol, a compound connected to vitamin D, is 15 days, though this doesn't take into account the percent of vitamin D stored in body tissue.

A more precise picture comes from studying the effects on calcidiol levels of a single dose of oral vitamin D over time. A study published in the American Journal of Clinical Nutrition determined that patients given a dose of 100,000 IU of vitamin D maintained elevated levels in their blood for longer than 84 days. However, this research doesn't consider the impact of vitamin D metabolized from sunlight.

Storage rates of vitamin D can also vary depending on many factors, including weight levels. For instance, some research indicates that obese subjects worked through their vitamin D stores more quickly than those of standard weights. Likewise, the vitamin D that was stored in their tissues was rarely released when needed.

Vitamin D Levels Go Down in Winter when Women are Sick

Research shows that your overall health might also impact how long vitamin D remains in your body throughout the winter months. For instance, one study found that women with health problems like diabetes and arthritis tended to have lower levels of vitamin D in the winter.

However, it's unclear at this time whether their low levels triggered their health problems, or whether the health conditions were instead responsible for their lower vitamin D absorption rate.

Which Vitamin D Exposure Level is Ideal?

While it's still unclear exactly how much vitamin D you can store in your body throughout the winter, the evidence shows that your levels depend on a variety of factors that include your skin type, location, summer exposure levels, and even overall health.

Health experts often state that any blood level of vitamin D below 30 ng/ml is low, and some go as far as raising that minimum to 70 ng/ml. Ideally, 40% of your skin should be exposed to sunlight for about half the time it would take to get a sunburn in summer months.

Sunscreen and covered skin will affect vitamin D production rates by as much as 95%, so it's necessary to ensure your skin is uncovered for maximum absorption. If ample sunlight isn't available, 5000 IU per day is considered safe and effective.

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