Most people are deficient in vitamin d, or at least they are for optimum health. Treat yourself to a d3 supplement from Aliment Nutrition (they sell online, and are very good) and take a couple a day. If you are a little overweight then you will need more vitamin d than someone who isn't overweight. Also make sure you get in the sun without sun cream on for about 20 mins a day (if you're in the uk at the minute, if you're somewhere the sun is stronger or you burn easily, cut the time down) and don't have a shower for half an hour or so after so you don't wash it off.
Good levels of vit d will increase your insulin sensitivity and bring your levels down. Apart from sugar (remember low fat products have loads of sugar in as well as the things you expect to be sugary, so eat natural - food with minimum processing) stress will have a big impact on your insulin levels too, and this might not be just 'argh I have too much to do' stress, but lack of sleep, lack of water, not enough me-time etc etc... So it's worth taking a look at those things too.
Have a read of the Insulin Factor by (I think) Anthony Haynes. Great book, well written and clear.
Do you take a good fish oil supplement too? That is great for insulin sensitivity. Aliment do the best quality and best value one around. I'm currently drinking a homemade juice with 3 teaspoons in, and I honestly can't taste it.
All this stuff is very much my 'thing' so shout if you need any more info, I'm very happy to help
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