To delay the onset of osteoporosis, women in their 30s and 40s can follow these four tips: 1. Maintain a balanced diet rich in calcium and vitamin D, such as dairy products, dark green vegetables, and vitamin D-rich fish. 2. Engage in regular weight-bearing exercises like brisk walking, running, or weight lifting to strengthen bone density. 3. Avoid smoking and excessive alcohol consumption, as these habits can accelerate bone loss. 4. Have regular health check-ups to monitor bone density changes and address issues early.