By Gary Goldfaden, MD and Robert Goldfaden
People today are aware of the importance of maintaining optimal blood levels of vitamin D for their overall health and well being. What many people do not know is that vitamin D is also indispensable to the health, beauty, and longevity of the largest organ in the body: your skin.
The problem is that while the body uses sunlight to make vitamin D, sun exposure itself accelerates skin aging. Over time, ultraviolet light damages the skin, leading to wrinkles, sun spots, and higher risk of skin cancer. In addition, much of the vitamin D produced in the skin is taken up and used by other systems of the body.
In this article, you will discover the critical role vitamin D plays in skin cell development and repair, as well as how it mobilizes your skin's immune system and helps destroy free radicals that can cause premature aging. You will also learn how topical vitamin D lotion can deliver benefits directly to your skin, preserving its softness, health, and youthful appearance.Shedding Light on Vitamin D's True Identity
Technically, vitamin D doesn't fit the classic definition of a vitamin at all. A vitamin is a substance that is crucial to normal everyday life function, but can't be synthesized in sufficient quantities by an organism, and thus must be obtained from the diet.1 Your skin has the ability to manufacture as much as 10,000 IU of vitamin D after 20 to 30 minutes of summer sun exposure.2 But there are many limiting factors to internal vitamin D synthesis that include age, skin color, geographic latitude, seasonal variation in sunlight availability, and the widespread (but necessary) use of sunscreen, which all make it difficult for your body to produce the vitamin D it needs for optimal health through sun exposure alone.
Too much sun damages the skin, creating wrinkles and fine lines, while increasing skin cancer risk. Still, your skin's ability to synthesize a portion of its daily requirement directly from sunlight3 makes vitamin D unique among all other nutrients.
Functionally speaking, vitamin D more closely resembles a hormone than a vitamin.4,5 Hormones are chemical messengers produced by certain glands and cells in your body that bind to specific receptors in order to produce a targeted biological response. The active form of vitamin D, calcitriol, is one of the most powerful hormones in the human body, endowed with the ability to activate over 2,000 genes (roughly 10% of the human genome).2 In order to become calcitriol, however, vitamin D must first undergo a complex series of biochemical reactions that begin in your epidermis, the outermost layer of your skin and the key to its youthful appearance.The Key Nutrient for Skin Cell Growth and Replacement
Being fat-soluble, vitamin D as calcitriol easily crosses the phospholipid membranes of your cells and migrates to the nucleus. Here it binds with vitamin D receptors,6 a special group of proteins that sense the presence of steroid hormones. This linking regulates the expression of genes that turn different cell functions on or off.7,8 Vitamin D receptors are directly involved in cell proliferation and differentiation, as well as optimal immune function. These issues are vitally important to your skin, which not only serves as your first line of defense against pathological invaders, but must also replace approximately 30-40,000 lost cells a minute.9
This constant loss of cells on your skin's surface must be offset naturally by an ongoing vitamin D- dependent renewal process that takes place in specialized cells called keratinocytes. Keratinocytes account for about 95% of all cells in your epidermis.10 They possess two properties which make them extremely valuable--the ability to actively divide, and the ability to differentiate. They are continuously providing new cells for replenishment of your skin's surface.
Cell activity in this layer is responsible for the creation of an underlying structural framework for your skin to reinforce the delicate matrix of skin tissue. This helps your epidermis form a watertight barrier that locks in moisture and keeps your skin soft and supple.
This is where vitamin D comes in: rates of cell division and differentiation are triggered by growth factors and other molecules that are controlled by the presence of vitamin D.11-13 If adequate amounts of vitamin D are not available, your epidermal cells won't differentiate optimally. As a result, the outer layer of your skin may become thinner and more fragile. It begins to sag from lack of adequate support. Dryness and wrinkles set in as moisture is gradually lost to the outside.14 This is one of the main reasons why vitamin D is absolutely essential to the maintenance of healthy-looking skin.
What You Need to Know: Skin Protection and Vitamin D
- In addition to overall health, vitamin D plays an integral role in skin protection and rejuvenation.
- In its active form as calcitriol, vitamin D contributes to skin cell growth, repair, and metabolism. It optimizes the skin's immune system and helps destroy free radicals that can cause premature aging.
- While the body can produce vitamin D on its own through sun exposure, too much sun accelerates skin aging. Over time, it can damage the skin, leading to wrinkles, sun spots--and increased risk of skin cancer.
- Age, skin color, geographic latitude, seasonal variations in sunlight availability, and sunscreen use make it difficult for your body to produce all the vitamin D it needs.
- Much of the vitamin D produced in the skin is also taken up and used by other systems of the body.
- Between the ages of 20 and 70, your skin loses about 75% of its ability to produce vitamin D3--the metabolic precursor to calcitriol.
- Along with optimal vitamin D intake, topical vitamin D application can exert a protective and rejuvenating effect on aging skin.
Skin Repair and Protection
What most people know as "the immune system" is actually one of two components of your body's total immune capacity. Known to scientists as the adaptive immune system, its ability to mount a strong defense against invading microorganisms and then retain protective antibodies for the future is vital to our survival.
Individuals also possess another immune system that serves as the body's first line of defense against bacteria, viruses, and other pathogens. Located partially in your skin, it is called the innate immune system. Its purpose is to recognize and repel all foreign invaders in a non-specific fashion, regardless of whether the particular pathogen has been encountered before or not. Innate immunity is so important that nature saw fit to preserve it through almost 60 million years of evolution. It is essential that we have an innate response not only to provide an immediate defense against pathogens, but also to reduce the painful inflammation caused by an overreaction of the body's immune system.
The skin is a crucial component of the body's innate immune system. The skin's keratinocytes can metabolize vitamin D to its active metabolites, while the enzymatic machinery of skin cells can help produce vitamin D receptors. Within the skin, vitamin D and its receptors help form an impermeable barrier and promote an innate immune response against foreign microbes.12
An intriguing study demonstrated one mechanism by which vitamin D may participate in innate immunity.15 After a skin wound occurred, keratinocytes surrounding the wound increased the expression of genes coding for antimicrobial receptors and the antimicrobial peptide, cathelicidin. The active form of vitamin D helped induce these gene expression changes, assisting the eradication of infectious invaders at the site of the skin wound. Vitamin D thus helps keratinocytes recognize and respond to microbes and protect wounds against infection.
Topical application of a vitamin D analog has been found to increase expression of the LL-37 antimicrobial peptide in human skin. LL-37 is a prevalent antimicrobial peptide expressed by keratinocytes that plays numerous roles in skin health, including: controlling microbial flora in intact and damaged skin, attracting immune cells, promoting epithelial repair, and supporting angiogenesis needed for skin healing. Decreased expression of numerous antimicrobial peptides has been reported in certain skin conditions such as atopic dermatitis and chronic leg ulcers.16
Together, these findings highlight vitamin D's crucial role in helping skin cells recognize and respond to invading microorganisms, protecting healing wounds against infection, and promoting skin healing.Sunlight, Heat, and Skin: The Intricate Process of Vitamin D Production
There are five distinct layers that make up your epidermis. These are (from outer to inner): the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Where vitamin D is concerned, however, it's the stratum basale and stratum spinosum that are the most important. These two layers contain the highest concentration of a substance called 7-dehydrocholesterol (about 25-50 micrograms for every square centimeter of skin).29 7-dehydrocholesterol absorbs UVB light wavelengths that are present in sunlight.
Ultraviolet-B (UVB) light breaks the B ring of 7-dehydrocholesterol's chemical structure to form what is called pre-D3. Pre-D3, a thermodynamically unstable molecule, then undergoes a heat-induced rearrangement to form the prohormone vitamin D3 or cholecalciferol.30
From here, vitamin D3 is transported to your liver, where it is combined with the 25-hydroxylase enzyme to form calcidiol (25-hydroxycholecalciferol or 25-hydroxyvitamin D). Once produced, calcidiol is stored in your liver until it is needed. Later calcidiol is released into the blood where it's transported to the proximal tubules of your kidneys. Here it is hydroxylated by another enzyme, 1-alpha-hydroxylase, to create the biologically active form of vitamin D, 1,25-dihydroxycholecalciferol or calcitriol. Following this conversion, calcitriol is released back into the bloodstream and carried to the various target organs of your body by binding primarily to vitamin D binding proteins (85-88%) and albumin (12-15%).31Fighting Age-Accelerating Free Radicals in Your Skin
Although your body metabolizes oxygen very efficiently, your cells still get damaged by reactive oxygen species (ROS)--reactive molecules that contain oxygen.17 This happens when an oxygen molecule sacrifices one of its electrons during chemical reactions inside your body. The oxygen molecule is then left with an unpaired electron in its outer orbit, making it highly unstable.18 This oxygen free radical has to reestablish its balance and form an octet (an atom with eight valence electrons), so it steals a neighboring electron from other natural proteins in your skin to regain stability. This sets off chain reactions that result in an aftermath of misshapen and broken molecules. In the end, the structure of your skin is damaged and its cellular structure is weakened.19,20 Free radicals initiate the deterioration of your skin's structural support and decrease its elasticity, resilience, and suppleness.
The most common oxygen free radicals are the singlet oxygen, the hydroxyl radical, and the superoxide anion, all of which are normally found in your skin because of its high rate of metabolic oxidation and the availability of fatty acids.21-23 However, other factors such as air pollution, alcohol consumption, cigarette smoke, and stress can increase free radical production as well.24
Stress not only generates potent, destructive free radicals--it also produces adrenaline-related products that restrict blood flow to your skin. Your skin is able to protect itself from this destructive oxidative stress through the use of low molecular weight antioxidants that combat free radicals. Among the most important of these is vitamin D. In fact, vitamin D has been found to be more effective in reducing lipid peroxidation and increasing enzymes that protect against oxidation than vitamin E.25,26
Unfortunately, between the ages of 20 and 70, your skin loses about 75% of its ability to produce vitamin D3--the metabolic precursor of calcitriol, the biologically active form of vitamin D.27 In addition, your skin is the last organ of your body that receives antioxidants from the food and supplements you eat.28 Much of the active vitamin D that your body produces is used to help build and maintain strong bones. However, if antioxidants are applied topically, protection for your skin can be enhanced.Summary
While most people now understand the importance of maintaining optimal vitamin D blood levels for its numerous health benefits, few know of its role in skin protection and rejuvenation. More a hormone than a vitamin, it is integral to the beauty, suppleness, and youthful appearance of skin. The complex process of vitamin D synthesis and utilization yields the active form, calcitriol, a hormone-like compound intrinsic to cellular proliferation and differentiation. Vitamin D thus contributes to skin cell growth, repair and metabolism. It mobilizes the skin's immune system and helps destroy free radicals that can cause premature aging. Between the ages of 20 and 70, your skin loses about 75% of its ability to produce vitamin D3--the necessary precursor to calcitriol. In conjunction with optimal intake of vitamin D3, topical vitamin D application may enhance its protective and rejuvenating effect on aging skin.
** While most people now understand the importance of maintaining optimal vitamin D blood levels for its numerous health benefits, few know of its role in skin protection and rejuvenation. **References
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