How to get healthy skin 1
Micronutrients and Skin Health
Nutritional status plays an important role in the maintenance of healthy skin (1-4). Macronutrients (carbohydrates, proteins, and lipids) and micronutrients (vitamins and nutritionally essential minerals) work together to maintain the barrier functions of skin in the face of everyday challenges. Changes in nutritional status that alter skin structure and function can also directly affect skin appearance. Unlike many organs, skin nutrition may be enhanced directly through topical applications. Topical application of micronutrients can complement dietary consumption, leading to a stronger, healthier protective barrier for the body. This article discusses the roles of select micronutrients and other dietary compounds in the maintenance of skin health. Topical use of these compounds is discussed, and the effects of micronutrient deficiencies in the skin are also covered.
Skin Structure
Skin provides a physical and chemical barrier between the outside environment and the inside tissues of the body (5, 6). This ‘barrier function’ is critical to protect underlying tissues from pathogens, chemicals, and environmental exposures (5, 7). Structurally, skin is comprised of two main layers, the epidermis and the dermis (Figure 1) (6, 7). The epidermis, the upper layer, is responsible for many of the barrier functions of skin. The dermis is the structural and nutritive support network underneath the epidermis. Since each layer has its own unique structure and function, the nutritive requirements of each must be considered separately.
Epidermis: the outer barrier
Human epidermis comprises the outermost layers of skin cells, ranging from 0.1 mm to 0.6 mm thick, depending on the location on the body (7). Keratinocytes compose the vast majority (90-95%) of cells within the epidermis. These cells are found in layers of varying size and thickness (6). The bottom or basal layer of the epidermis consists of a layer of round, undifferentiated keratinocytes that is supported by contact to the underlying dermis. Cells in this layer are constantly dividing in order to produce new cells that will make up the remainder of the epidermal layers (6, 7). Thus, it is in this fashion that skin is replenished, with new cells from the basal layer replacing the outer layer of skin cells that is shed over time.
Once a keratinocyte leaves the basal layer, it begins the process of cell differentiation known as keratinization (6). During keratinization, keratinocytes undergo several morphological changes that result in the synthesis of unique structural proteins (especially keratin) and the secretion of a variety of specialized lipids that will comprise key components of the epidermal barrier. These cells also undergo a process known as cornification, in which the synthesized proteins are assembled in an envelope just inside the cell membrane (5-7). At the end of this process, the large protein-laden cells, now known as corneocytes, lose their nuclei and other cellular organelles. Thus, there is little metabolic activity present in the outer layers of the skin (often referred to as ‘dead’ cells).
The outermost layer of skin, the stratum corneum, interacts with the outside environment. Lipids secreted by cells during the keratinization process are now assembled with extracellular proteins into a protective layer. This barrier is often likened to a ‘brick and mortar’ system: large, flattened, metabolically inactive corneocytes (the protein-rich ‘bricks’) are sealed together with a variety of extracellular lipids and proteins (the ‘mortar’) (5, 6). The chemical properties and structural design of this layer slow absorption and limit penetration of the skin, as well as limit the loss of vital nutrients and water from the underlying tissue. As new layers of cells are produced, the outer cells of the stratum corneum are enzymatically detached from this layer and shed in a process called desquamation (5).
Further, other cells contribute to the function of the epidermis. Melanocytes are cells that produce melanin, a compound involved in skin pigmentation produced in response to ultraviolet (UV) light exposure (6). Melanin can absorb energy from UV light to shield underlying tissues from damage. Langerhans cells are antigen-presenting cells involved in epidermal immunity. Merkel cells have various neuronal and endocrine roles; these cells function as mechanical sensors and produce growth factors that regulate sweat glands, hair follicles, nail growth, and nerve function in skin (6).
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