Vitamin D is primarily produced in the skin through exposure to ultraviolet B (UVB) rays from sunlight. However, the amount of vitamin D the skin can produce is affected by several factors, including latitude.
Latitude is a key determinant of vitamin D production from sunlight:
– In the northern hemisphere, latitudes above 37 degrees north (e.g. Boston, New York) receive insufficient UVB radiation from the sun during the winter months to stimulate vitamin D synthesis in the skin.[1][4]
– At latitudes above 37 degrees north, the sun’s rays hit the earth’s surface at a very oblique angle during the winter, meaning the UVB rays do not penetrate the atmosphere effectively.[5]
– People living at higher latitudes are at greater risk of vitamin D deficiency, especially during the winter, due to the reduced UVB exposure.[3]
– In contrast, regions closer to the equator (latitudes below 33 degrees) have more consistent year-round UVB exposure and vitamin D production.[3]
However, latitude is not the only factor – other influences like cloud cover, pollution, skin pigmentation, and time spent outdoors also affect how much vitamin D the body can produce from sunlight exposure.[2][3] Dietary intake and supplementation may be necessary to maintain adequate vitamin D levels, especially for those living at higher latitudes.
In summary, latitude is a major determinant of vitamin D production from sunlight, with higher latitudes associated with reduced UVB exposure and increased risk of vitamin D deficiency, particularly during winter months.[1][3][4]
Vitamin D from Summer Sun
The skin can produce vitamin D from the sun’s UVB rays during the summer months up to latitudes of around 37 degrees north or south of the equator[1][6][7]. At latitudes above 37 degrees, vitamin D production in the skin is minimal or non-existent for most of the year, except for a few summer months[1][6].
For example, in the United States, the region above 37 degrees north latitude (shaded area in the map) experiences very little vitamin D production in the skin during the fall, winter, and spring seasons[1]. People living in these higher latitude areas are at greater risk for vitamin D deficiency[1].
However, even in southern latitudes below 37 degrees, vitamin D production can be suboptimal if people spend little time outdoors or use sunscreen regularly[7][8]. Factors like skin pigmentation, clothing, and sun-seeking behaviors also impact vitamin D status[8].
While the skin can produce vitamin D from the sun during summer months up to around 37 degrees latitude, vitamin D deficiency remains common worldwide due to various lifestyle and environmental factors[7][8].
Know Your Latitude
Latlong.net is an online geographic tool that can be used to lookup latitude and longitude of a place, and get its coordinates on a map. You can search for a city, address, or click on the map to find the latitude and longitude. For example, the cities of Santa Cruz, Gilroy and Madera in California are at about 36 degrees latitude. Roughly anything north of San Francisco (which spans about 37.7 to 37.8 degrees latitude) is above 37 degrees.
Foods Rich in Vitamin D3
The best foods for vitamin D3 are primarily found in animal sources, particularly fatty fish and fish liver oils. Here are some of the top sources of vitamin D3 from [17]:
1. Rainbow Trout, Farmed: 3 ounces provide 645 IU (81% of the Daily Value (DV)).
2. Sockeye Salmon: 3 ounces provide 570 IU (71% of the DV).
3. Sardines: One can provides around 200 IU.
4. Egg: One egg provides 44 IU (6% of the DV).
5. Beef Liver: 3 ounces provide 42 IU (5% of the DV).
Additionally, other fatty fish like halibut and mackerel are also good sources of vitamin D3[18].
Tanning Beds vs Vitamin D3 Supplements
The World Health Organization classifies tanning devices as carcinogenic, while vitamin D3 supplements are a safe way to obtain the vitamin[10][11]. While tanning beds may increase vitamin D levels, the health risks from UV exposure outweigh any potential benefits. Vitamin D3 supplements provide the vitamin safely without the carcinogenic effects of artificial tanning devices.
Avoid Hypercalcemia, Take K2 as MK7 with your D3 Supplements
To avoid hypercalcemia and the potential risks of high vitamin D intake, it’s recommended to take vitamin K2 as MK-7 along with your vitamin D3 supplements[12][14][15][16].
Vitamin D toxicity can lead to excessively high calcium levels in the blood (hypercalcemia), which can cause calcium and phosphorus to accumulate in blood vessel linings (blood vessel calcification)[12]. This calcification is associated with an increased risk of heart disease[12].
Vitamin K2, particularly the MK-7 form, helps direct calcium into bones and teeth where it’s needed, while inhibiting calcium deposition in soft tissues like blood vessels[13][14]. Studies have shown that vitamin K2 as MK-7 can improve bone mineral density, bone strength, and cardiovascular health when taken for at least 2 years[14].
To support bone health while minimizing heart disease risk:
– Limit calcium supplements to 500 mg daily
– Take 180-300 mcg of vitamin K2 as MK-7 daily
– Get vitamin D from sun exposure or supplements (1000 IU D3 daily is safe for most)
– Ensure adequate magnesium intake to support vitamin D activation[13]
Vitamin K2 is found in natto, cheese, butter from grass-fed cows, and some other fermented foods[2][4]. Combining vitamin D3 and K2 supplements may provide the most benefit for bone and cardiovascular health[14][16].
Always consult your doctor before starting any new supplements, especially if you take blood thinners or other medications, as vitamin K can interact with some drugs[13][16].
Citations
[1] https://www.health.harvard.edu/staying-healthy/time-for-more-vitamin-d
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4525738/
[3] https://www.emro.who.int/emhj-volume-27-2021/volume-27-issue-3/effect-of-latitude-on-seasonal-variations-of-vitamin-d-and-some-cardiometabolic-risk-factors-national-food-and-nutrition-surveillance.html
[4] https://www.chsbuffalo.org/sites/default/files/images/education/JAOA-vitamin-E.pdf
[5] https://sunsaferx.com/blogs/health-wellness/vitamin-d-and-sunlight-how-to-know-if-your-sun-exposure-is-producing-vitamin-d
[6] https://www.health.com/37th-parallel-vitamin-d-deficiency-8364004
[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10239563/
[8] https://www.emro.who.int/emhj-volume-27-2021/volume-27-issue-3/effect-of-latitude-on-seasonal-variations-of-vitamin-d-and-some-cardiometabolic-risk-factors-national-food-and-nutrition-surveillance.html
[9] https://www.sciencedirect.com/science/article/pii/S1011134406002491
[10] https://pubmed.ncbi.nlm.nih.gov/30811696/
[11] https://www.skincancer.org/blog/ask-the-expert-can-a-tanning-bed-safely-provide-me-with-the-vitamin-d-i-need/
[12] https://www.healthline.com/nutrition/vitamin-d-and-vitamin-k
[13] https://blog.encompasshealth.com/2019/08/28/calcium-without-k2-is-a-heartbreaker/
[14] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4566462/
[15] https://www.protocolforlife.com/k2-mk-7-d3/
[16] https://health.clevelandclinic.org/too-much-vitamin-d
[17] https://www.webmd.com/diet/foods-high-in-vitamin-d3
[18] https://www.healthline.com/nutrition/9-foods-high-in-vitamin-d
[19] https://nutritionsource.hsph.harvard.edu/vitamin-d/
[20] https://www.dietaryguidelines.gov/resources/2020-2025-dietary-guidelines-online-materials/food-sources-select-nutrients/food-sources
[21] https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/