Blog Directory - Blogged foodliterate: May 2009

Monday, May 18, 2009

The ABC's of Vitamins - Vitamin D

And so we come to Vitamin D, which had been the object of some squabbling over whether it should even be called a vitamin (the other camp voted for it to be a hormone), but alas, a vitamin it became. Vitamin D is a fat soluble vitamin like vitamin A, and it has two primary forms: ergocalciferol (D2) and cholecalciferol (D3) both of which are secosteroids.

D2 is the form found in plants and is created by the irradiation (from the sun, not a lab) of ergosterol in the plant. D3 is the form people produce through photosynthesis in the skin by activation of the sunlight on 7-dehydrocholesterol. (And you thought only plants performed photosynthesis!) Both D2 and D3 are biologically inactive and have to be converted to their hormonal (thereby active) forms through two hydroxylations to create dihydroxylated vitamin D.

Not all solar rays have the required energy to penetrate the epidermis and create vitamin D3, so there are a number of factors that affect the production. First, we need UVB rays, which we also know are related to skin cancer, so sunscreen (with a SPF as low as 8) does reduce the amount of vitamin D produced. Also, skin pigmentation plays a role; while pale ol’ me needs only about 15-30 minutes of exposure, someone who has very dark skin may need 3 hours to produce an equivalent amount of vitamin D.

Age also plays a role in the production of vitamin D, the younger you are, the more vitamin D is produced in the skin. As we age, our epidermis thins out and negatively affects our ability to photosynthesize. Luckily we can get our vitamin D from supplementation (recommended: 200 IU/day if you are under 50, 400 IU/day if you are over 50, and 600 IU/day if you are over 70). Just be aware, there is no toxicity from naturally produced vitamin D, but there is the chance of toxicity from supplements – at high levels it can cause hypercalcaemia and ultimately kidney failure. We can also get vitamin D from fortified milk, fatty fish, egg yolks and butter.

What does vitamin D do for us? It is required for the homeostasis of calcium and phosphorus, bone remodeling (takes minerals away and puts them back to create new bone), and the modulation of cell proliferation (increase in number) and differentiation (different kinds of cells). Vitamin D also plays a role in our immune system like macrophage activation (those cells that gobble up pathogens) and as an immunoregulator (your T-cell response). Perhaps best known is its relationship with calcium; they are inextricably connected, calcium absorption depends on vitamin D.

Well, we have covered all of the water soluble and half the fat soluble vitamins. Only vitamins E & K are left to tackle. I'm going to be taking a quick vacation for the Memorial weekend so look for my next post around the end of May or beginning of June. Until then, eat well & be well!

Monday, May 11, 2009

The ABC's of Vitamins - Vitamin C

Vitamin C. This is one where you are probably thinking, “Please, I know all about Vitamin C why even bother…”. And you might be correct, but I’m guessing there are some things about Vitamin C of which you may not be aware or that you may at least find interesting. Let’s see if I’m correct.

Vitamin C is the generic term for ascorbic acid and dehydroascorbic acid. It is a water soluble vitamin like the B vitamins we’ve been discussing. Ascorbic acid is found freely in your plasma and is distributed to all the cells of the body, especially the adrenal and pituitary glands. It is also stored in the brain where it functions as a neuromodulator, is involved in myelination and in the biosynthesis of noradrenaline (a neurotransmitter).

Ascorbic acid aids in inorganic iron absorption by acting as a chelator and reducing agent (this converts the iron to its ferrous state which is more soluble). In fact, taking vitamin C with a meal can increase your iron intake by around 6 fold. Ascorbic acid is required for the biosynthesis of carnitine (needed for the production of energy in your mitochondria) and enhancement of prostaglandin synthesis (modulates cardiovascular, pulmonary, immune and reproductive functions). Ascorbic acid also prevents the formation of N-nitroso compounds (aka nitrosamines, found in cured meats) which have been implicated in gastric cancer. Ascorbic acid stimulates collagen production as a co-factor in the polypeptide chain which aids in wound healing.

Perhaps one of ascorbic acid’s best known roles is that of antioxidant; it is an aggressive scavenger of free radicals. Lesser known, but of great interest to those of us who are allergy sufferers, is its role in the degradation of histamine. It decreases blood histamine levels thereby acting as an antihistamine.

Deficiencies are rare, but mild scurvy is seen in alcoholics & drug addicts, where it is manifested as weakness, lethargy, shortness of breath, and aching joints and muscles. Hopefully you are all getting the recommended daily intake of 90mg from citrus fruits, strawberries, papayas, dark green leafy vegetables and broccoli. If not, there are a world of supplements out there from both natural and synthetic sources (both have good bioavailability). If you are getting your vitamin C from supplements, it is better to take many small doses throughout the day rather than one large dose. You can also increase your absorption of supplemental vitamin C by taking it with a meal.

So, do you feel like you know this vitamin a little better than you did before? Good, now we will move on to Vitamin D it should be D-lightful!