Americans love their vitamins. Go into any grocery store or newsagent in New York and by the cash till, you can impulse-buy not Walnut Whips but little plastic bags of vitamins and boosters for about a dollar each. For the quintessential New York experience, buy one of these packets and visit your nearest juice bar. There you can order a freshly-made fresh carrot/ginger juice and wash down those eight or so enormous pills, smug with the knowledge you've just experienced a health-kick that is helping to kick-start the American economy.

Last year in the US, vitamin and health-food sales rose by 22.7 per cent - continuing the trend of continuous annual double-digit growth since 1991. The health foods industry now has an annual turnover worth $7.55 billion, making it one of the largest and fastest-growing areas of the American economy.

British visitors to America have increasingly latched on to the fact that America is the place to buy vitamins; they're cheaper, more abundant in range, and often chemically more sophisticated (a yearly avalanche of new products includes Ester-C , which appears to have isolated the good qualities of vitamin C without any of the supposed "side-effects").

Anyone visiting New York to shop should consider buying vitamins - even if it does mean rattling your way through customs, feeling halfway between a drug-addict and a hypochondriac. But before you buy vitamins in New York, there are one or two things you should know. All New York vitamin stores have permanent discounts of around 20 per cent - all of them. Don't blame the staff if they appear unhelpful. It's illegal for them to offer you anything approximating medical advice. However, a friendly sales assistant in the smaller shops will probably give you advice off the record, but make it clear you understand they are not "prescribing".

Most vitamin shops will point you to some well-thumbed books usually piled up on the counter. The best place to go for browsing through books is Angelica's Herbs on 147 First Avenue, which has a virtual library at their customers' disposal, as well as 9,000 herbal products.

There are now Tesco-sized versions of Holland & Barrett in America, but you won't find any of these in town. Go to the smaller and mid-sized shops; you'll be less bewildered by the range, which is still about 5,000 products even in the most modest stores. This ranges from face cleansers to frightening- looking colon-cleansing kits in bucket-sized bottles.

Choose a decent multivitamin first. You can go for a solitary familiar brand like Twinlabs or Solgar (cheapest offer on Solgar v2000 is to be found at a shop called Ayurverda on 129 1st Av at $18.40 for 90 tablets). Another good brand is Living Source ($42 for 180 "food state" tablets at Infiniti 1 Astor Pl); go for "food state" multivitamins if you can afford them - they're made from plant extracts and are more readily absorbed in the gut.

I usually buy my multivitamins at one of the most ubiquitous chain-stores in New York (this time their Nutri-100 at $16.95; buy one get one half- price). It goes under the name of the Vitamin Shoppe (strange how many of these shops have Culpepper-ish archaisms for names), with 15 branches throughout Manhattan. It's rather like Boots, and is a business set up in the Eighties by the pharmacologist Jeff Howard interested in the discounting of bulk-bought vitamins.

After you've got your multivitamin, look around for a robust anti-oxidant. Anti-oxidants mop up cellular damage caused by stress and pollution; they are the perfect city-dwellers' pill. As with multivitamins, the choice is bewilderingly specific: no Crooke's one-a-day round here. Co-Enzyme Q-10 is probably the most popular antioxidant on the market. A fine crystalline substance made only in Japan, it's already famous for its mind-boosting qualities and use in pyschoactive drinks sometimes sold (legally) in nightclubs. Currently The Vitamin Shoppe have an offer on their own-brand 30mg capsules, with 40 per cent off their whopping $74.95 price tag (for 300 tablets).

After you've got the multivitamins and anti-oxidants, be experimental. How about some Vitamin Shoppe caffeine-free Super Energy Up ($12.95), which includes a whole lot of Chinese herbs (including ma huang) for pepping you up with a bit more fizz than Gurana? How about some extra B6 for PMS? Or what about some Bee Granules product, which contains propolis, pollen and royal-jelly (though an 80-year-old Sicilian bee-keeper once told me the only effective bee remedy was the anti-viral propolis).

Of particular interest are the native American herbs, rarely seen in the UK, including Black Cohosh (asthma) and Chaparral (antioxidant). Sarsaparilla has been used by bodybuilders for non-steroid muscle development. Saw Palmetto is used for "honeymoon cystitis - irritation due to excessive sexual activity".

In the end, it's hard to say how effective any of these products are, and in England, there tends to be more cynicism among scientists as to how many vitamins we need. I've always held the line that if there's even the slightest chance of pills making me feel better, and maybe avoiding bouts of flu, they're worth the price of a newspaper every day. Enjoy the crazy pluralism of America at its craziest and most life-affirming with its current flowering in the health-food industry. But don't take it all too seriously.

Best for American herbs: Angelica's Herbs, 147 First Av, NYC (529 4335).

Best small shops: Infiniti Health, 1 Astor Place, NYC (979 8000) and Health Shoppe, 579 Broadway (966 2730).

Vitamin Shoppe: 145 Spring St/666 Lexington Av/1193 3rd Av (966 3463).