Vitamin D. Do You Need to Supplement?

Time of day, season, and latitude all determine the amount of sunshine (UVB rays) that reaches your skin to make Vitamin D. When the Sun’s rays enter the Earth’s atmosphere at too much of an angle, the atmosphere blocks the UVB portion of the rays. This occurs during the early and later parts of the day, during the winter season and increases as you move further away from the equator. A good rule of thumb is: If your shadow is longer than you are tall you are not making much vitamin D.

Vitamin D Winter and latitude
Vitamin D Winter is when no vitamin D production is possible due to the atmosphere blocking all UVB. This lasts for several months, with the time increasing as you move further from the equator. Seattle is at 47 degrees, the Vitamin D Winter months for Seattle is around November through early March.

Other factors

  • Dark-skinned individuals need up to six times longer in the sun than those with light skin because their skin has more melanin content. Melanin is Nature’s built-in protection against skin damage from excess ultraviolet exposure and so it allows less UV to enter the skin.
  • Amount of skin exposed – at least 40% of the entire skin surface should be exposed for optimal vitamin D production. The torso produces the most, legs and arms some, hands and face very little or none at all.
  • Age – vitamin D synthesis can take up to 4 times as long for those over the age of 60 and under the age of 20.
  • Altitude – more UVB is filtered out of the atmosphere at the beach as opposed to a mountain top.
  • Cloud cover – water droplets in the air scatter some UVB back into space.
  • Air pollution — particles in the air (such as ozone, haze, and sulfur dioxide) can either absorb UVB or reflect it back into space.
  • Being behind glass – glass blocks all UVB.

How Much to Take
The amount needed of Vitamin D for one person may not be enough for another, due to age, weight, absorption, overall health, genetics and amount of sun exposure. The only way to know for sure if a certain dosage is working for you is to have your vitamin D level tested. It is a simple blood test.

Vitamin D Council recommends the following amounts of supplemental vitamin D3 per day in the absence of enough sun exposure.

  • Healthy children under the age of 1 years – 1,000 IU.
  • Healthy children over the age of 1 years – 1,000 IU per every 25 lbs of body weight.
  • Healthy adults and adolescents – at least 5,000 IU.
  • Pregnant and lactating mothers – at least 6,000 IU.

Additionally, children and adults with chronic health conditions such as autism, MS, cancer, heart disease, or obesity may need as much as double these amounts. Please consult with your physician

Oil vs. powder
Vitamin D3 supplements come in two forms:

  1. oil (cod liver oil-based) – fat-soluble vitamin D, includes liquid drops or gel caps.
  2. dry powder (lanolin-based, from lamb’s wool) – water-soluble vitamin D, includes capsules or tablets.

Both water-soluble and fat-soluble vitamin D appear to be equally absorbed and metabolized by the body.

Is there a vitamin D for vegans?
Vitamin D3 is produced by animals in response to ultraviolet B (UVB) exposure. Vitamin D2 – what some call “vegetarian vitamin D” – should not be considered a satisfactory alternative. Those who opt to take this form should know that vitamin D2 is not real vitamin D. It is not the same substance as vitamin D3 produced in human skin and may have actions in the body different to those of vitamin D3.

People with some health conditions should only take vitamin D with the guidance of a physician, if you have a health condition please contact your physician before taking Vitamin D supplements.

Vitamin D and Cancer
The link between vitamin D sufficiency and a decreased risk in cancer is promising. A randomized controlled trial found a 77% reduction in all-cancer incidence when the study group supplemented with 1100 IU/day of vitamin D plus 1450 mg/day calcium. Epidemiologist Dr. William Grant,the founder of the nonprofit organization Sunlight, Nutrition and Health Research Center, states “based on various studies of UVB, vitamin D and cancer to date, it appears that the global cancer burden can be reduced by 15-25% if everyone had vitamin D blood levels above 40 ng/ml.”



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