Vitamin D Factsheet

Sun Exposure and Vitamin D Synthesis

Vitamin D is mainly obtained through sunlight, and it is recommended that we get 10 minutes of sun exposure at the hottest time of the day, every day.  During these 10 minutes, we should have as much skin exposed as possible and avoid using sun cream.  However, sun exposure should be safe so after 10 minutes it is advisable to apply sun cream to prevent skin damage.  Here’s a brief introduction to vitamin D, how it is processed in the body and how it may be good for us.

Introduction to Vitamin D and its Processing

Vitamin D has two forms; ergocalciferol (D2), which is produced in plants through the conversion of ergosterol by ultraviolet light, and cholecalciferol (D3), which is produced in animals through the conversion of cholesterol by ultraviolet light.  D3 is found naturally in oily fish and less so in eggs, and D2 is added to some foods such as cereal.  The main source of vitamin D in humans is not through the diet, but from exposure to the sun, which converts a cholesterol derivative into vitamin D3.  Both D2 and more effectively D3 are then converted in the liver to 25-hydroxyvitamin D (25-OHD), stored and when needed to be converted in the kidneys to 1,25 dihydroxy vitamin D (1,25-(OH)2D3), also known as calcitriol.  Vitamin D then binds to vitamin D receptors, of which there are many, to become active.  As you can see, it’s a long and complicated process!  

Research and Insights into Vitamin D Function

There has been a lot of research into the function of vitamin D over the last few years, and although it is still in its infancy it makes for interesting reading.  Here’s just a snapshot:

  • An association has been proposed between vitamin D deficient pregnant women and an increased risk of pre-eclampsia (a condition in pregnancy that includes symptoms such as high blood pressure and protein in the urine), as well as an increased risk to the baby of being diagnosed with diabetes mellitus 1 in childhood and of being of low birth weight.  
  • There is also a large amount of evidence that vitamin D supplementation during the first year of life could reduce the chances of getting diabetes type 1.
  • Also worth mentioning is vitamin D’s importance in the prevention of bone disorders in both pregnant and lactating women and rickets in infants and children.  
  • One of the mechanisms currently being explored links vitamin D deficiency to an increased risk of cancer, particularly breast, colorectal and prostate cancer.  
  • There is a current debate as to whether vitamin D deficiency is associated with an increased risk of neurological disorders such as Parkinson’s disease and Alzheimer’s disease, or whether a deficiency influences the progression of these conditions.  
  • Well documented is vitamin D’s link with other neurological conditions such as multiple sclerosis, memory impairment and depression in older adults.
  • Studies also suggest a link between vitamin D and heart disease.  

Managing Vitamin D Levels in Winter

Whilst it’s recommended that we build up our stores of vitamin D in the summer, due to the lack of sunlight in the winter, half of the vitamin D in these stores will have decreased within 4-6 weeks of being produced, so if you ever needed an excuse to go somewhere nice and exotic during the winter, you’d be hard-pressed to find a better one than this!  If that’s a no-go, then supplementing with good quality vitamin D through the winter months, whilst not as enjoyable as lying on a beach, can be just as effective!

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