This felt fitting to be my first blog post as summer is here and in full force (southern states know)! Speaking for my fellow Texans, we experience 100+ degree weather for a good three months and for most, that means avoiding the sun's rays, lathering up on sunscreen, and doing your best to stay cool. These tactics are great in theory and by all means, do what you must to stay hydrated and comfortable. But let’s actually dive into some facts about the sun and understand how sun exposure, even in the summer, is beneficial!
The first thing to understand is skin type, age, sun quality, and diet will ultimately determine one’s tolerance to sun exposure.
Skin Type
Many go by the Fitzpatrick chart, as shown below, to determine the length of time in the sun required for the body to produce optimal Vitamin D levels. As per Craig A. Elmets, MD, someone with skin type III sitting in the sun around noon in Miami can synthesize 1,000 IU of Vitamin D in 6 minutes during summer and 15 minutes during winter. Someone with skin type V requires 15 during summer and 29 minutes during winter. The same comparison in Boston is approximate to sun exposure times in Miami during summer months, however in winter months, skin type II would require 1 hour and skin type V would require 2 hours to synthesize 1,000 IU of Vitamin D. Elmets concluded that even someone with Fitzpatrick type I skin would find it impossible to receive enough sun to synthesize just 400 IU of Vitamin D after 2 pm in Boston’s winter months.
Photo Source: https://tribecamedspa.com/fitzpatrick-skin-type-chart/
Age
A study exposed healthy young adults and older adults with the same amounts of UVB radiation from a tanning bed. Six young adults ages 20 to 30 showed an increase of Vitamin D3 in their blood level to be 3x’s higher than six older adults ages 62 to 80, thus demonstrating the decrease in the skin’s capacity to create Vitamin D3 as one ages.
A young adult wearing a swimsuit and exposed to one minimal erythemal dose (MED) of UV radiation in a tanning bed was equal to taking a ~20,000 IUs Vitamin D2 supplement. When the same study was performed on a healthy 75 year old man but exposed to UVB radiation in a tanning bed 3x’s a week for 7 weeks, he raised and maintained his blood levels of 25(OH)D into the healthy normal range of ~50 ng/ml, which is the same concentration as measured in the young adult.
Sun Quality
If you live in a big city, you are unfortunately familiar with air pollution. Nitrous oxide and ozone are the two main pollutants most common in large cities, and absorb solar UVB radiation, thus reducing the sun exposure effectiveness for the skin to produce Vitamin D.
Altitude can also play a role in sun exposure absorption. The higher the altitude, the shorter the UVB path must travel and therefore, the skin can produce more Vitamin D3 in a shorter timespan.
Diet
It is possible to increase your melanin production, and thus change your skin type over time through dietary changes. Polyunsaturated fatty acid (PUFA) metabolism are macronutrients that can influence the production of eicosanoids/bioactive lipids, and modulate cell signaling, gene expression and oxidative stress in the epidermis. Data suggest that an omega-6 PUFA loaded diet could increase oxidative damage in melanocytes with a long-term net outcome of accumulated mutations and increased risk of skin cancer, specifically melanoma. Separate post on this topic to come!
Synthesized Vitamin D vs. Ingested Vitamin D
Vitamin D3 produced in the skin lasts up to 3 times longer than oral ingestion because it takes approximately ~8 hours for previtamin D3 to fully transform into Vitamin D in the skin, and even more time for Vitamin D3 to enter the dermal capillary bed. When Vitamin D3 is produced in the skin, 100% of it is potentially bound to the Vitamin D binding protein. Ingested Vitamin D3 from diet or supplementation gets incorporated into chylomicrons which are transported first into the lymphatic system and then the venous system. Only ~60% of the Vitamin D3 is then bound to the Vitamin D binding protein and ~40% leftover is rapidly cleared in the lipoprotein bound fraction.
Sun Exposure and Vitamin D Toxicity?
After direct sunlight exposure, the skin can only convert ~15% of 7-dehydrocholesterol to previtamin D3. Any further exposure will result in photoequilibrium where previtamin D3 is either converted into lumisterol3 and tachysterol, or reverted back to 7-dehydrocholesterol. When Vitamin D3 is made in the skin from solar UVB radiation exposure, it will absorb the UVB and convert into several suprasterols (formation product of Vitamin D2) and 5,6-trans-vitamin D3 (another member of Vitamin D3 derived from Calciol). Vitamin D intoxication can not occur from excess sun exposure due to excess previtamin D3 and Vitamin D3 being photodegraded into calcemic activity byproducts.
Serotonin and Melatonin
Did you know melatonin and serotonin are positively correlated? Studies have shown that mammal’s skin cells have receptors for both serotonin and melatonin, and serotonin produced in the skin is transformed into melatonin. Higher serotonin levels result in a more positive, calm, and focused mental outlook. High serotonin levels in relation to melatonin production results in shorter nights and longer days due to longer UVR exposure. We all know seasonal depression occurs in the winter months where the days are shorter and we receive less sunlight. SAD is linked to lower serotonin levels during the day and delayed melatonin production at night. Speaking for the modern American lifestyle, more people suffer from suboptimal melatonin production due to more time indoors and late nights. Melatonin researcher Russel J. Reiter of the University of Texas Health Science Center stated that summer day light can be a thousand times brighter than any light experienced indoors, therefore, people who work indoors should 1) get outside periodically and 2) sleep in total darkness, as this will majorly impact one’s melatonin rhythms and improve mood, energy, and sleep quality. Even wearing sunglasses outside further limits the full sunlight exposure the eyes need to create optimal melatonin rhythms. Just 10 to 15 minutes of shade free sunlight exposure can improve one’s health.
Additional Sun Dependent Pathways
The sun may be best known for boosting production of Vitamin D, but there are many other UVR-induced effects completely separate from this pathway.
PREVENTING AUTOIMMUNE DISEASE: UVA and UVB exposure can have direct immunosuppressive effects through upregulation of cytokines (TNF-α and IL-10) and increased activity of T regulatory cells that remove self-reactive T cells.
INCREASED IMMUNE FUNCTION AND PREVENTING MELANOMA: With sun exposure, melanocytes and keratinocytes in the skin releases Alpha melanocyte-stimulating hormone, otherwise known as α-MSH, which has shown to improve immunologic tolerance and suppression of contact hypersensitivity. α-MSH also helps limit oxidative DNA damage resulting from UVR and increases gene repair, thus reducing melanoma risk, as reported 15 May 2005 in Cancer Research.
COMBATING MAST CELL ACTIVATION SYNDROME: Calcitonin gene-related peptide (CGRP) is released in response to both UVA and UVB exposure. This potent neuropeptide modulates a number of cytokines and is related to impaired induction of immunity and development of immune tolerance. As stated in the September 2007 issue of Photochemistry and Photobiology, mast cells (which mediate hypersensitivity reactions) play a crucial role in CGRP-mediated immune suppression. This might help explain sunlight’s efficacy in healing skin disorders (e.g. psoriasis and eczema).
INCREASED IMMUNE RESPONSE: Neuropeptide substance P. Along with CGRP, this neuropeptide is released from sensory nerve fibers in the skin following UVR exposure. This results in increased lymphocyte proliferation and chemotaxis (chemically mediated movement) but may also produce local immune suppression.
ENDORPHIN CREATION: UVR increases blood levels of natural opiates called endorphins. As stated in the June 2003 Journal of Investigative Dermatology, melanocytes in human skin express a fully functioning endorphin receptor system, and a study published 24 November 2005 in Molecular and Cellular Endocrinology suggests that the cutaneous pigmentary system is an important stress-response element of the skin.
Get Your Daily Sun Exposure!
Now you know more about the factors that can influence sun exposure and how the sun is extremely important for Vitamin D3 production and optimal health. Sitting outside for three hours in prime sunlight until you are burnt to a crip is not the move though. So how do you stay protected when outside for longer periods? Finding shade, wearing protective clothing, hats, sunglasses, and utilizing sunscreen when needed are your answers. Not all sunscreens are equal though. On July 14th 2021, the FDA recalled certain Neutrogena and Aveeno sunscreens that contained the cancer causing chemical, benzene. As a precursor for the next blog post, I will leave you with this tip: read and understand ingredient labels on anything you ingest or have skin-to-skin contact with!
FUN FACTS:
It can be difficult to obtain enough Vitamin D from diet as most food sources do not contain high levels of D. Some indiginoug groups like the Inuits, are an exception as this population consumes oily fish, seal and whale blubber, and polar bear liver, all which contain high levels of the vitamin. Unless you would consider yourself an Inuit or are getting at least 15 minutes of adequate sun exposure each day, supplementing Vitamin D is recommended.
Vitamin D is a fat soluble vitamin, therefore once ingested or produced in the skin, it gets incorporated into the body fat and is transported to the liver for 25(OH)D conversion. Take Vitamin D supplements with food (and even better if you include it with a fat like avocado)! The Endocrine Society suggests all adults receive a daily dosage of 1,500 to 2,000 IUs of Vitamin D for optimal health.
Vitamin D deficiency increases susceptibility to autoimmune diseases, poor immunity, mental health disorders, and cardiovascular problems. Maintaining healthy Vitamin D levels has shown a decreased risk in depression, Alzheimer disease, epilepsy, and neurocognitive decline.
Female health and obstetrics is one area I am extremely interested in, so this fact was especially intriguing to me. Cesarean sectioning became a common practice in the late 1800’s for the delivery of healthy children of mothers who had suffered from Vitamin D deficiency in utero. These mothers were born with a Vitamin D deficiency and infantile rickets which resulted in flat pelvis’ and small pelvic outlets. These females had normal fertility levels but still had difficulty delivering through their vaginal canal. Today, pregnant women with Vitamin D deficiencies have a 400% increase in likelihood for a C-Section.
Citations:
Elmets, Craig A. “How Much Sunlight Is Equivalent to Vitamin D Supplementation?” NEJM Journal Watch: Summaries of and Commentary on Original Medical and Scientific Articles from Key Medical Journals, 4 June 2010, https://www.jwatch.org/jd201006040000002/2010/06/04/how-much-sunlight-equivalent-vitamin-d.
Wacker, Matthias, and Michael F Holick. “Sunlight and Vitamin D: A global perspective for health.” Dermato-endocrinology vol. 5,1 (2013): 51-108. doi:10.4161/derm.24494, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897598/
Cario-André, Muriel et al. “Polyunsaturated fatty acids partially reproduce the role of melanocytes in the epidermal melanin unit.” Experimental dermatology vol. 14,3 (2005): 194-201. doi:10.1111/j.0906-6705.2005.00273.x, https://pubmed.ncbi.nlm.nih.gov/15740592/
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