Economic gradients Loneliness 1 Social isolation 1 Social support 1 UK Biobank 1 aged 1 article 1 biobank 1 controlled study 1 economic status 1 female 1 follow up 1 human 1 human experiment 1 loneliness 1 major clinical study 1 male 1 probability 1 sample size 1 social isolation 1 social support 1