Nutrition Lecture 6: Vitamin D Flashcards
What is the main source of Vitamin D?
The sun!!
What are some food sources of Vitamin D?
Cod liver oil, Sardines, Smoked salmon, Eel/tuna, some dairy
What is essential to make vitamin D?
Cholesterol is essential to make vitamin D, but we still need to be careful about having too much
What type of reaction is the action of creating Vitamin D from sunlight on the skin?
Non-enzymatic reaction
What is the precursor for Vitamin D?
7-dehydrocholesterol forms vitamin D3
What are the three different types of sunlight radiation?
UVC, UVB, UVA
What is UVC?
The shortest wavelength, absorbed by the atmospheric ozone
What is UVB?
Has the largest effect on the top layer of skin, causes redness/burning, SKIN CANCER
What is UVA?
The longest wavelength, reaches deep into the layers of skin, causes aging/wrinkling
Most sunlight that gets through is….
UVA
What radiation is of most use and most concern?
UVB
What behavioural factors affect Vit D status?
Clothing, sunscreen, time of day, time spent outdoors, supplements, diet
What does global dietary Vitamin D uptake?
The mandatory food fortification countries have good vitamin D intake levels (Canada, USA) - Most other countries are not over AI
What are host-related factors that affect Vit D status?
Skin colour, age, sex, BMI, genetic differences
What is melanin?
Melanin is a natural pigment responsible for the coloration of skin, hair, eyes.
Where is global skin colours the darkest?
In countries closest to the equator
Melanin is a natural protection of what?
The harmful effects of UV light
What is one of the negative effects of melanin?
Have to spend more time in the sun to get sufficient Vit D
What are environmental factors that affect Vit D status?
Season, latitude, altitude, clouds, pollution
How does latitude affect vitamin D?
As latitude increases (moving towards the poles), the angle of the sun’s rays becomes more oblique, and the intensity of UVB radiation decreases
What are the two major forms of Vitamin D?
D2 and D3
Where do we get D2 from?
Plant foods and fungi
Where do we get D3 from?
Animal foods
What does D2 start out as?
Ergosterol
How does ergosterol become D2?
- Starts out as ergosterol
- Beta ring is broken down by UVB light
- This forms Pre D2, with a broken ring
- Then with the addition of heat it dorms vitamin D2
What does D3 start out as?
7-dehydrocholesterol
How does 7-dehydrocholesterol become D3?
- Beta ring is broken by UVB light
- This forms Pre D3, with a broken ring
- Then with the addition of heat it forms Vitamin D3
What is the main differences in structure between D2 and D3?
Extra double bond and methyl group on D2
Why is D3 more effective than D2?
D2 has lower affinity for the Vitamin D binding protein, therefore is cleared faster from circulation
Both D2 and D3 are transported in the blood via what?
Vitamin D Binding Protein (DBP)
What type of vitamin is Vitamin D?
Fat-soluble
What does vitamin D require to be absorbed?
Fat
Where is vitamin D absorbed?
In the upper small intestine
How is vitamin D absorbed in the small intestine?
By non-saturable passive diffusion
How is Vitamin D transported from the intestine to the liver?
by vitamin D binding globulin
What facilitates the absorption of vitamin D?
Mixed micelles
How do mixed micelles facilitate the absorption of vitamin D?
by solubilizing it in the watery environment of the small intestine, allowing for efficient uptake by intestinal cells.
Where is vitamin D soluble?
In the hydrophobic core of mixed micelles
Is vitamin D from food or skin biologically active?
NO - requires metabolic activation in the body
How is vitamin D made biologically active?
Either forms (D3, D2) Needs to be transported to the liver and then the kidney
What happens when Vitamin D3/D2 is transported to the liver?
D3/D2 is converted into 25(OH)D = calcidiol
What is the name for 25(OH)D?
Calcidiol
What is the biomarker of vitamin D status?
Calcidiol
Is calcidiol the active form?
No, needs to be transported from the liver to the kidneys to be activated
What happens when Calcidiol is transported to the kidneys?
Calcidiol is converted into 1,25(OH)2D = Calcitriol
What is the name for 1,25(OH)2D?
Calcitriol
Is calcitriol the active form?
Yes!
What is the vitamin D status of NZ adults?
68% = Sufficient
27% = Insufficient
5% = Deficient
What is vitamin D status by season?
- Great levels in summer
- Decreases as winter comes closer
- Parts of spring still low but starting to improve
What is vitamin D status by ethnicity?
Maori and pacific:
- Less likely to get sunburnt
- Less likely to be forming Vitamin D
What is vitamin D status by age and sex?
Women are lower than men
Males tend to stay the same or get higher with age
Women tend to get lower with age
What is vitamin D status by region? (North vs South)
Northern region has the lowest prevalence of vitamin D deficiency
What are rickets?
inadequate mineralization of growing bones in children, resulting in soft, weak bones and skeletal deformities
What is osteomalacia?
softening of the bones due to impaired mineralization of the bone matrix in adults
What is osteoid?
The bone protein matrix (primarily collagen)
Does excessive sun exposure cause vitamin D toxicity?
No, sustained heat on skin degrades pre-vitmain D3 and D2
