The Truth About Vitamin Supplements

The toxic truth about vitamin supplements: How health pills millions take with barely a second thought can do more harm than good

GLUCOSAMINE

WHAT IT IS: The supplement, which is made from crab and lobster shells (so should be avoided if you have a seafood allergy), is often taken to ease the symptoms of arthritis.

POTENTIAL SIDE-EFFECTS: According to the Arthritis Research Campaign, these can include stomach upset, constipation, diarrhoea, headache and rash; glucosamine can also react with anti-diabetic treatments by increasing blood sugar levels.

The UK Commission on Human Medicines has noted that glucosamine has a negative interaction with the blood-thinning drug warfarin and warns against taking these substances simultaneously.

The supplement might also cause water retention, as it attracts water.

KELP

WHAT IT IS: This supplement is made from a seaweed which is the fastest-growing marine algae in the world - it can grow two feet in one day and is most abundant off the north California coast.

Kelp is a rich source of several minerals and trace elements, including iodine - deficiency of which can lead to an underactive thyroid. It is marketed as a treatment for thyroid imbalance, caused by the thyroid gland producing either too much or too little of the hormone.

POTENTIAL SIDE-EFFECTS: Despite the claims made for it, studies have linked kelp to an increased risk of thyroid dysfunction. It's also a blood thinner and shouldn't be taken with aspirin or any medicine to lower blood pressure.

There's also concern that some kelp is being harvested from kelp 'forests' in polluted oceans, which means it could be toxic. In 2007, research at the University of California found high levels of arsenic in eight out of nine kelp supplements. Arsenic is linked to hair loss, headaches, confusion and drowsiness.

POTASSIUM

WHAT IT IS: Maintaining an adequate potassium level is important for bone health and the proper functioning of the body. Potassium supplements are often taken to help combat insulin resistance, arthritis and menopausal symptoms such as fatigue and mood swings.

POTENTIAL SIDE-EFFECTS: Taken in very high doses as a supplement, potassium can have serious side-effects such as arrhythmia (faulty heartbeat) - and it can even be fatal.

Research at Oregon State University has also linked it to muscle weakness, confusion, stomach pain and numbness or tingling in the hands, feet or mouth.

Potassium supplements react badly with some medicines, and shouldn't be taken by anyone suffering from kidney or heart disease, severe dehydration or high blood pressure.

Older people who often have too much potassium in their bodies should avoid these supplements - kidneys are less efficient at eliminating potassium as we age.

MELATONIN

WHAT IT IS: Natural melatonin is a hormone made by the pineal gland in the brain and helps to regulate sleep.

Supplements can control our sleep/ wake cycles and are used to treat sleep disorders. British manufacturers make medical claims about its sleep benefits, so here it is licensed as a prescription- only medicine - however it is freely available in the

U.S. POTENTIAL SIDE-EFFECTS: These include raised blood pressure, vivid dreams, headache, lower body temperature, fatigue, depression, decreased libido and reduced fertility.

A daily dose of 1- 3 mg of melatonin increases the body's levels of melatonin by 20 times the normal amount. The British Pharmaceutical Society says that studies on its effectiveness to treat jet-lag have been conflicting.

CALCIUM

WHAT IT IS: Calcium is an essential mineral for the growth and maintenance of healthy bones and teeth and for blood clotting, muscle contraction, healthy nerves and good hormone function. It is usually taken by women to boost bone health.

POTENTIAL SIDE-EFFECTS: Research published last month by Auckland and Aberdeen universities reflected other studies in finding a 30 per cent increased risk of heart attack among women taking calcium supplements - most women taking them are postmenopausal and concerned about osteoporosis.

This increase is due to the risk of calcium supplements accelerating the hardening of blood vessels. Doctors involved with a 2008 New Zealand study advise women of 70 or older not to take calcium supplements.