I'm shocked at the junk that vitamin C preparations contain, and what on earth is 'microcrystalline cellulose'? Is there such a thing as straight vitamin C?

Extra ingredients or 'excipients' are needed to make tablets easier to swallow, say, or to preserve ingredients. These should be natural and either inert or add nutritional value. Microcrystalline cellulose comes from plants and is used to bind and give bulk, and as an anti-caking agent. Basic vitamin C is plain ascorbic acid, but it is not effectively absorbed. Ester C, however, is unique in that it has a neutral pH and is more easily utilised. Lifetime Ester C 650mg has no unnecessary excipients; £14.95 for 90 capsules (0800 389 8195).

I read with interest your reply regarding vitamin supplements for people with macular degeneration (January 24). At 32p a day, the formulation you mentioned seems to be rather expensive, particularly as many people with the condition (where the macula, or central part of the retina, responsible for acute vision, deteriorates) are elderly and on limited incomes.

Fresh, colourful fruits and vegetables contain the antioxidants lutein and zeaxanthin that protect the macula from age-related deterioration. In a US survey it was found that six or more servings a day of these foods protected against MD.The publication Proof! this year surveyed lutein supplements for quality and price. Higher Nature's Visual Eyes was highly rated, with well above the minimum daily recommendation at 30mg of both lutein and zeaxanthin; it costs 25p a day (0870 066 0808). The least costly, at 11p a day, and a just-adequate 6mg of lutein, was from Holland & Barrett.

· Emma Mitchell is a natural health therapist. Before following Emma's recommendations, you should consult your GP about any medical problems or special health conditions.

Send your questions to Wellbeing, Guardian Weekend, 119 Farringdon Road, London EC1R 3ER. Email: ask.emma@theguardian.com.