I have tried creams, oils, powders, buffing, soaking in almond oil, vitamins B and D tablets and always wear gloves when washing up or cleaning with a bucket of water.
My nails are nice for the last three days or so of August and start to break off on 1 September. By Christmas they are in shreds. At Easter they are not much better and now, some time after Whitsun they are beginning to neaten up and grow again.
I was talking to my hairdresser last week about this and she said her nails had never been good but she recommended a nail oil which seems to work better than most.
The trick is to apply it every time you wash your hands, so at least 6 times a day, and to massage it in thoroughly. I have now got some of this and will try and get into the habit of massaging. It's my last hope. I've been fighting this battle since I was at least 16 and I'm 70 this year!
I also recently had my bloods checked and Vitamin D was deficient although I was taking vitamin D supplements. I have doubled the dose so maybe that will help.
The tablets I was taking were 1000 i.E. (not sure if that is a German abbreviation) but I have seen that you can get up to 25000 over the counter!