Why is Vitamin D so Important?

By Brooke Bulloch, RD

Known as the “sunshine vitamin”, vitamin D plays an important role in the body, but are Canadians getting enough?

Vitamin D Physiology

There are two ways the body attains vitamin D: through the skin and through the ingestion of food or supplements.

When the bare arms and legs are exposed to sunlight, a substance in the skin called 7-dehydrocholesterol absorbs UVB radiation and is converted to pre-vitamin D3, a biologically inactive form of vitamin D (keep reading, it doesn’t stay this way).

When we consume vitamin D from food or supplements, it is also in a biologically inactive form. Whether absorbing vitamin D from the sun or ingesting it, inactive vitamin D will eventually become active vitamin D through 2 hydroxylation steps – the first in the liver and the second in the kidneys. After this point, vitamin D is active and the body can put it to use.

Vitamin D’s Role in the Body

Vitamin D is most known for its role in bone health. It supports calcium absorption, and helps to maintain adequate calcium and phosphate levels in the blood. This allows for normal bone mineralization, bone growth, and bone remodeling throughout different stages in life. Vitamin D helps to prevent the disease rickets (soft, misshapen bones) in children and osteoporosis (thin and brittle bones) in adults.

Vitamin D also plays an important role in the body’s immune system, managing inflammation, cell growth, neuromuscular function, and glucose metabolism. Preventing or correcting vitamin D deficiency can be protective in many ways.

How Much do you Need?

According the Institute of Medicine and Health Canada, children age 1 to adults age 70 require 600 IU per day, including those who are pregnant or breastfeeding. This increases to 800 IU for those older than 70. The Tolerable Upper Intake Level is currently set at 4000 IU per day for all adults.

Food Sources

Not many foods contain vitamin D. A few Canadian-specific foods sources include:

• Egg yolk: ~35 IU/egg
• Salmon or trout: ~500-600 IU/3 ounces
• 1 x 85g can of sardines in oil: ~600IU (note amounts can vary due to sardine sun exposure and whether it’s canned in oil vs water)
• Fortified milk: 100 IU/1 cup
• Fortified soy beverage: 80 IU/1 cup
• Non-hydrogenated Margarine: ~60 IU/ 1 tbsp

Are Canadians Getting Enough?

Statistics Canada suggests one third of Canadians have insufficient serum vitamin D levels. There may be a few explanations for this:

• Sun exposure for vitamin D is not a reliable source.
  • Protecting your skin from the harmful effects of UV rays is important, and wearing sunscreen will greatly reduce vitamin D synthesis in the skin.
  • People with naturally darker and black skin tones require 3-5 times longer in the sun to make the same amount of vitamin D as someone with fair or white skin tones.
  • Canada’s northern latitude makes it tricky to synthesize vitamin D all year long. Between October and April, the UVB rays are not strong enough and we’re protecting our bodies from colder weather. Your body will not store enough vitamin D to get you through until the next spring and summer.
• Based on the food sources listed above, unless you’re eating salmon or sardines every day, it’ll be tough to meet vitamin D needs with food alone. Also, Health Canada advises that children consume no more than 750 ml or 3 cups of milk per day. That is only enough to meet half of a child’s daily vitamin D needs.

Should You Supplement?

Currently, Health Canada recommends that breastfed infants are supplemented with 400 IU of vitamin D per day, and that people over 50 years of age also supplement with 400 IU of vitamin D per day. Many other Canadians are unlikely to be meeting vitamin D requirements from sunshine and diet alone. While a vitamin D supplement may be necessary, it is always best to speak first with your family’s health care provider about supplementation.