The NOS was founded in 1986, since when its mission has been to raise awareness about the brittle bone disease. But despite its efforts, nearly 20 percent of respondents in the survey said they eat less calcium than they did in 1986.
This trend was set against a back-drop of general healthier eating, which two thirds saying they eat more organic foods and fewer preservatives.
This may mean that calcium-rich foods, such as dairy products, have come to be viewed as 'bad'; certainly dieters have a tendency to avoid fatty foods.
But calcium is also found in other, 'less obvious' foods, such as baked beans, tofu, green leafy vegetables, bony fish and dried fruit.
Most dieticians recommend that people adopt sensible, balanced eating habits to lose weight and increase their exercise, rather than cutting out entire food groups.
Jackie Parrington, spokeswoman for the NOS said: "Calcium, vitamin D and other important minerals to build and strengthen our skeleton can be obtained from many different foods, like cereal, bread and fruit. This is another reason why it's important to eat a balanced diet."
Moreover research has shown that vitamin D plays a very important role in aiding absorption of calcium. In the wake of a spate of positive study results of vitamin D, several retailers, including Tesco, have reported as much as a four-fold increase in sales of vitamin D supplements in the last few months.
Vitamin D is found naturally in a few foods, such as oily fish. It is also made by the skin on exposure to sunlight.
The NOS survey was carried out by tickbox.net, but the organisation has not publicised full details of participant numbers or their age groups.
It did say that 80 percent of over 55s said they were not concerned about osteoporosis - a surprising result given that nearly half of women and one in five men over 50 will break a bone as a result of osteoporosis.
The daily recommended intake of calcium in the UK for healthy adults is 1,000 mg. For teenagers the RDI is 1,300mg to help them achieve critical bone density, and for those over age 50, who are at greatest danger of osteoporosis, 1,200mg.
Osteoporosis is estimated to affect about 75 million people in Europe, the USA and Japan. According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is € 31.7 billion in Europe, and 17.5 billion in the US (2002 figure). The total annual cost of osteoporosis in the UK alone is over £1.7 billion (€ 2.5 billion), equivalent to £5 million (€ 7.3 million) each day.