The Collison Newsletter September 2012


                          VITAMIN  D  and  SUNLIGHT*

Health Benefits of Vitamin D 

Regular exposure to sunlight allows our skin cells to use the ultraviolet B rays to synthesise vitamin D, which has a number of health benefits.

  • Vitamin D helps the intestines absorb nutrients, including calcium and phosphorus, resulting in strong bones and a strong immune system. 
  • Vitamin D prevents osteomalacia (brittle bones and weak muscles) and rickets (skeletal deformity in children). 
  • Vitamin D aids the correct calcium balance in the body that prevents osteoporosis and arthritis. 
  • Vitamin D assists in optimum functioning of the immune system. It increases the white cell production. 
  • Vitamin D also has other widespread effects on the body. Vitamin D regulates blood pressure, reduces stress and tension, relieves body aches and pains by reducing muscle spasms, reduces  respiratory infections, aids insulin secretion, helps fight depression, improves overall skin health by decreasing wrinkles, makes the skin soft, strong and smooth and improves cardiovascular strength by providing a protective lining for the blood vessels. 
  • Vitamin D has also been shown to support prostate health. 
  • Vitamin D is recommended as part of the treatment of cancer, diabetes, hyperparathyroidism, osteomalacia and fibromyalgia.


Sunlight is the light of the sun, sunshine. In the broad sense, it is the total frequency spectrum of electromagnetic radiation given off by the sun.


The spectrum of electromagnetic radiation striking the Earth's atmosphere spans a range of about 100 nm to 1 mm. (A nanometre, nm, is a billionth of a metre). This can be divided into five regions, in increasing order of wavelength:

  • Ultraviolet C, 100 - 290nm. (Ultraviolet refers to the fact that the radiation is at a higher frequency than violet light [the end of the visible range ... red, orange, yellow, green, blue, indigo and violet] and hence invisible to the human eye). 
  • Ultraviolet B, 290 - 320nm. 
  • Ultraviolet A, 320 - 400nm.
  • Visible range, 380 - 780nm.
  • Infrared range, 700nm - 1mm. (Infrared A 700 - 1400nm, infrared B 1400 - 3000nm and infrared C 3000nm - 1mm). 

Sunlight, the Skin and Vitamin D

  • Ultraviolet C

Since Ultraviolet C is mostly absorbed by the ozone layer of the atmosphere, so that very little reaches the earth, it has no significant effect on the skin with sun exposure.

  • Ultraviolet A

Ultraviolet A (UVA) accounts for about 95% of the UV radiation reaching the earth's surface. Hence it is significantly more prevalent than ultraviolet B (UVB).


UVA has equal intensity during all daylight hours, throughout the year (ie it is non-seasonal).


It can penetrate clouds and glass.


It penetrates skin more deeply than UVB.


UVA causes skin ageing and wrinkling (photo-ageing). It damages the keratinocytes which are found in the basal layers of the dermis, which is where most of the skin cancers (basal cell carcinoma and squamous cell carcinoma) occur. (Basal and squamous cells are types of keratinocytes.)


It does not cause significant reddening of the skin.


It also causes immune suppression.

  • Ultraviolet B

Ultraviolet B (UVB) causes skin reddening and sunburn. It penetrates only to the base of the epidermis, not to the base of the dermis (the bottom layer of the skin).


The intensity of UVB varies by time of day, season and location. In Australia the maximum intensity is between October and April, between 10am and 4pm, especially 12 midday and 2pm.


UVB rays do not penetrate glass.


UVB stimulates the formation of Vitamin D in the skin. The UVB converts cholesterol in the skin to Vitamin D. The skin cannot produce Vitamin D in the absence of sunlight. It is an efficient process. It is estimated that up to 5,000 international units (iu) of Vitamin D can be produced per minute of exposure. Thus, depending on how much of the skin is exposed to sunlight, the geographical location, the season and time of day (and hence the amount of UVB rays), 20 - 30 minutes will produce about 10,000 iu of Vitamin D.


Too little UVB exposure will lead to a lack of Vitamin D.

In a process called melanogenesis, UVB stimulates the production of melanin (the pigment of tanning), thus leading to tanning. Direct DNA damage by UVB is required to initiate this process. There is a 2-3 day lag phase for tanning to occur. Tanning gives increased protection from UVA and UVB, as the melanin absorbs the radiation and dissipates the energy as harmless heat. With more melanin, longer exposure to UVB is needed for vitamin D production. 

UVB causes limited DNA damage, which is recognised by the body and is repaired by the body. However, too much exposure will lead to excessive DNA damage (beyond that which results in the production of melanin, which is a healthy response), sunburn and possibly skin cancer.


The Vitamin D produced in the skin by UVB is mainly on or near the surface of the skin. Washing with soap and water, especially immediately after sunbathing, will remove much of the Vitamin D from the skin. It apparently takes 2-3 days for the Vitamin D to be fully absorbed. Soap removes much more than plain water. It is suggested that, after sunbathing, soap only be used under the arms and in the genital area.


The ideal source of Vitamin D is exposure to sunlight. Full body sun exposure quickly leads to the production of Vitamin D, maximised before the skin turns pink. Further exposure after that does not increase the production of Vitamin D significantly.


It is generally recommended that exposure to the sun should be early morning or late afternoon, for up to 2 hours. It is, however, best to have but a brief exposure, 10-15 minutes, to as much of the body as possible, about the middle of the day (when UVB is highest), without allowing the skin to turn pink. This shorter time will minimise UVA exposure (which is uniform throughout the day) while giving maximum UVB exposure and its benefits.


If sun exposure is not possible, it is wise to consider taking a Vitamin D supplement, especially if the blood levels of Vitamin D are less than optimal. This is more likely to occur in winter, and when day-time outdoor activities are minimal.


Vitamin D levels: sufficiency >75 nmol/L, suboptimal levels 50-75 nmol/L, insufficiency 25-50 nmol/L and deficiency 15-25 nmol/L.


*Copyright 2012: The Huntly Centre. 

Disclaimer: All material in the website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.


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