I know magnesium is really more of a mineral than a vitamin but I hope someone can help anyway.
I've had a long term problem with muscle stifness in my neck and shoulders due to my job using a computer most of the day. I tried lots of things but surprisingly I found magnesium to be quite helpful at relaxing muscles. Unforutnatley I also tend to drink a lot of coffee (which I hope to quite or at least reduce) and since caffeine depletes the body of minerals I imagine my body's magnesium levels are pretty low right now. I've been eating magnesium rich foods for a few days but to more quicky build up magnesium reserves I want to take supplements. Unfortunately where I live in the uk the choice of magnesium supplements is pretty limited and only magnesium oxide and magnseium trisilicate are readily available in stores. Unfortuantely i've read on some web sites that magnesium oxide is *not* a recommended way of taking magnesium, and i'm not sure if magnesium trisilciate is really a proper way to get magnesium. (chemistry lessons were a loooong time ago!) if anyone could clear up the matter i'd appreciate it! :)
I don't know if you have a supplement there called SLO-MAG. It contains a balance of the proper proportions of Calcium and Magnesium Chloride and is slowly released. I have fibromyalgia with terrible cramping and stiffness in my legs, neck and shoulders and it has helped me tremendously. It makes me very relaxed so I take it at bedtime and I sleep so much better, due to its relaxing effect. Hope this helps.
I've experimented with several magnesiums myself. What I found is that spray on magnesium products work faster and better than oral magnesium supplements. Trying to do high doses of oral magnesium would give me diarrhea. I've confirmed that this is common with most people. The topical stuff didn't cause this problem.
Some of the spray on magnesiums I tried were unpleasant and uncomfortable. I ended up sticking with a product that says it contains "magnesium chloride hexahydrate". I found this one to be the most comfortable and fastest acting.
I live in North America so it's pretty easy to get it here. You mentioned you live in the UK, so I found a shop in the UK that has it. They're called Aggressive Health. In the US, a company called Sunfood has a really good one too.
I've used this one for a few years and it always gets rid of my muscle twitches every time I put it on.