I've been charting my food intake for the past couple weeks, and just looked at the RDA (recommended daily allowance) charts for the vitamin content. Everything is pretty well at or way above 100% - except vitamin D.
In the UK, unlike the US, dairy products and even soy products are not fortified with vitamin D. Now the usual super source of this vitamin is the Sun. In the winter, what with (a) going out less and (b) having more skin covered when we do go out and (c) having really crap grey days, our key source of Vitamin D goes, well, out the window.
This loss of Le Sol means it's a good idea to supplement our supply.
Why?
Vitamin D is a HUGE important vitamin. It's major known role is enabling utilization of calcium. Calcium is not only critical for bone building, but also in muscle building. Without calcium, something called the myosin/actin bridge which enables muscle contraction can't work. But the main role of vitamin D is to let calcium work for bone building. It's also being shown as important for boosting the immune system and having a big impact on SAD (seasonal affective disorder).
So how get that extra boost of D and how much do we need?
Vitamin D is tricky to get from food despite the fact that we need so little of it a day relative to other vitamins and minerals.
5 micrograms a day if your under 50; 10 from 50 to 70, and 20 from 70+
To put this in perspective: a microgram is a millionth of a gram. Most other vitamins and minerals are measured in milligrams, or a thousandth of a gram. The difference is like that between a kilogram and a tonne. Not nothing. And therefore amazing to think that such a tiny amount is (a) so hard to get and yet (b) so important.
As for sources: cod liver oil rules. Cod liver oil is one of the all time best sources of vitamin D. 3.5 ounces of cooked salmon will get you your daily requirement; 3 ounces of tuna will also do it, but when you're not eating either of these fishes each day, get a supplement. You can also get a calcium + vitamin D tablet from Boots.
The advantage of a cod liver oil pill, especially if you're already getting enough calcium, is that besides getting vitamin D you also get vitamins A and E AND those wonderful omega three fatty acids EPA and DHA - not quite as many of them as found in a typical fish oil pill, but heh if you take a fish oil cap or 2 with each meal already, swapping one of those pills for cod liver oil during the winter is a great idea.
And not just for the calcium assistance property. Your grandma was right when she said "take cod liver oil and you won't get a cold" Vitamin D has been shown to impact resistance to influenza in kids in particular. Also at least one study has shown that temporarily upping to the daily amount of vitamin D for a month had a greater impact on seasonal affective disorder than the usual full spectrum light therapy. The dose increase was substantial (200 IU units is the RDA; the study used 100 thousand IU's for a month. As the note on the study says, more studies need to happen to confirm this work).
All things considered, its' highly likely that folks in the UK are actually vitamin D deficient. When considering how important vitamin D is for our winter health, finding ways to ensure we get enough - whether upping fish intake, or cod liver oil or taking a pill - at least for the winter till the sun comes out, and we get out into the sun, getting that Vitamin D somewhere is critical.
UPDATE DEC 08: it seems the RDA of Vit D is WAY LOW especially for folks in more northerly/colder climes where we see little sun, and our skin is exposed to little sun. There's a debate of anywhere from 2000IU to 15,000 IU's a DAY, but suffice it to say, that 200IU is at least 10 times too little. Time to look for bigger capsules. If you find a UK source for same, please let me know.
