Dietary supplements are big business, with around half of the Australian population using at least one type per year; most commonly a multivitamin and mineral pill. Many people take supplements as a form of dietary insurance in case they are not meeting their nutrient needs from foods alone. Others take them as a form of health insurance to protect against certain diseases. Some just take them out of habit. Supplements do have a role to play in some situations. People with a diagnosed deficiency, those with malabsorption conditions, women planning pregnancy, and people with very poor diets all can benefit from specific nutrient supplementation. But what about the benefit of supplements across the broad population? The mantra of most health professionals, which is even etched on the label of many supplements, is that supplements may only be of assistance if dietary sources are lacking. To see if this is supported by solid evidence, a systematic review of 63 clinical trials involving some form of supplementation in non-pregnant adults was carried out by a team of medical researchers. The clinical trials were broad in their nature with many nutrients studied including vitamins A, B6, B12, C, D and E; folic acid; calcium; selenium, omega-3 fatty acids; ginkgo biloba; glucosamine; saw palmetto; and milk thistle. All of the studies were randomised controlled trials and evaluated a range of health outcomes including risk of heart disease, cancer, diabetes, bone fractures, cognitive function and all-cause mortality. From the 63 studies, no benefit was seen in 45 studies with 10 of these showing a trend towards harm and just two showing a trend towards a benefit. Of the remaining studies, four showed harm with a greater risk of cancer with beta-carotene and a higher risk of fractures with a once-yearly dose of vitamin D. One study showed a lower risk of cancer with selenium supplementation, but this was not validated in much larger trials. Twelve studies showed a benefit and these mostly involved vitamin D... According to the above context, answer the following question. When are supplements mainly of assistance to people?

Options:
(a). When there is a risk of cancer
(b). not enough information
(c). after the diagnosis of heart disease
(d). when dietary sources are inadequate
Answer:
(d).